Ionic semiconductor materials and applications thereof

ABSTRACT

An electrode comprising: metallic electrode material; and a nonporous solid composite material encapsulating the electrode material, the composite material comprising an inert matrix material having hydrogel substantially uniformly dispersed therein, the hydrogel comprising 10% to approximately 50% by weight of the dry composite material, there being sufficient bonding between molecules of the hydrogel and the matrix material to prevent substantial leach-out of hydrogel molecules from the composite.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.275,977 filed Nov. 25, 1988, now abandoned. Application Ser. No. 275,977was a continuation-in-part of application No. 915,994 filed Oct. 6,1986, now U.S. Pat. No. 4,797,190.

BACKGROUND OF THE INVENTION

(1) Technical Field of the Invention

This invention relates to nonporous and non-diffusive, polymeric ionicsemiconductor materials which can function as novel highly selectivepermeable membranes driven by ionic depletion gradients and to a methodfor making such membranes. More particularly, the present invention isdirected to materials which have isolated catenated water moleculesformed on dispersed and bound hydrogel molecules contained within aninert nonporous nonpermeable matrix, such materials thus having theapparent ability to split water into its constituent ions, and theirapplication as a pervaporative material or in keeping two electrolytesseparate while transferring specific ions. The invention is alsodirected to methods and materials for use in the establishment ofreversible chemical-electrical/electrical-chemical energy conversions.Accordingly, the general objects of this invention are to provide noveland improved methods, materials and apparatus of such character.

(2) Description of the Prior Art

Proton selective transport membranes have been of general interest for anumber of years since many electrochemical half-cell reactions can belinked with a proton exchange. One of the first known uses of a protonselective membrane was in an early battery known as the Daniell cell.The Daniell cell utilized two separate electrolytes and electrodes,e.g., Zn/ZnSO₄ and CuSO₄ /Cu. A membrane was employed to maintainseparation between the metal ions while allowing the free passage ofprotons. The Daniell cell was not widely used since the best availableseparator for the cell was an animal membrane with a relatively shortlife. An attempt was made to substitute fragile, bulky ceramics for theanimal membrane in a Daniell cell, but such ceramics were ineffectiveover extended periods of usage since they allowed eventual mixing of themetal ions through diffusion. The Daniell cell was also not expected tobe a secondary or rechargeable battery since in its time it was the onlysource of electrical power.

Modern proton conductors assume the form of very thin fused glassmembranes, such as used in pH sensors, or salts, such as LiN₂ H₅ SO₄,KHF₂, and NH₄ CIO₄ which are not sufficiently conductive at roomtemperature to be useful in most electrochemical applications. In allknown proton conductors, a limited amount of water is known to bepresent. The water either contributes to or provides an active center ormedium for proton transport. Many natural or biological membranes areknown to conduct protons at room temperature with fair conductivities,but in general are not suited for commercial application due to theirlack of availability or poor chemical and thermal stability.

In U.S. Pat. No. 3,883,784 entitled "Electrical Device With HighDielectric Constant", assigned to the inventor of the present invention,an electrical device having a pair of conductive sheets with a layer ofan organic polymeric association product sandwiched between these sheetsis disclosed. The patented device functions because of limited protondisplacement from bound proton donors. The dried association productpreferably comprises polyethylene oxide of a high concentration, i.e.,between 60 and 90% by weight of the total, and a polymeric resinpreferably a phenolic compound.

U.S. Pat. Nos. 3,390,313 and 3,427,247, respectively entitled"Electromechanical Devices Using Ionic Semiconductors" and"Electroviscous Compositions", disclose a proton conductive coating onsilica which operates through proton acceptor and donor sites.

Polymeric permselective membranes do not have specific ion selectivitybut rather have variable permeability to specific groups of ions such asanions or cations. Further selectivity may be based upon ionic size,hydration, activity, etc. Selectivity is due to pores of limited sizecontaining isolated charge centers within the pore walls. The chargecenters may be furnished by introduction of ion exchange monomers. Someexamples of permselective membrane materials are: sulfonated poly-(styrene-divinyl benzene) copolymer, perfluorinated ionomers containingsulfonate and/or carboxylate active sites, or a copolymer of acrylicacid and divinyl benzene. In these polymers, the active charge ionexchange radical appears at various intervals along the polymeric chainresulting in random isolated charges. Accordingly, the distance betweenthe charge sites in such polymers is important since if they are tooclose swelling of the pores results and if they are too far distantinsufficient selectivity is obtained.

Pore size is a basic problem in producing polymeric membranes and mostthick film or solid processes involve use of an additive called a poreformer, which may be a solvent which evaporates leaving a porous or freevolume.

Hydrogels which are characterized by having a high degree of waterabsorption or the ability to modify water have been employed inelectrolytes. Such hydrogels have the ability to modify or immobilizethe electrolyte and to form a physical barrier to the migration ordiffusion of materials through the structure without significantlylowering the conductivity of the electrolyte. Hydrogels have been usedhistorically as thickeners, film forming agents or as barriers. Forexample, in drug delivery systems an active drug can be carried in anopen immobilized structure of electrolyte and hydrogel. The rate ofdiffusion of the drug through the structure is controlled by thecharacteristics of the selected hydrogel. The porosity andhydrophilicity of hydrogels can be decreased by cross-linking thehydrogel or by copolymerizing two different hydrogels. As anotherexample, hydrogels have been used in batteries to provide a barrierwhich will allow the diffusion of ions, absorb the electrolyte, provideelectronic separation and keep the solid particles or constituentsseparate. The most widely used hydrogel materials have been starches,cellulosics, and natural gums--all of which absorb many times their ownweight in water or electrolyte and form gels. These hydrogels also havea high diffusion rate which is important in most applications to singleelectrolyte systems.

Polymeric "nonporous" membranes are typically thin films with diffusionthrough the free volume offered by the amorphous phases of the physicalstructure of long chain polymers. Cellulose and its derivatives areexamples of materials which, when in film form, exhibit such behavior.Aromatic polyamide-imides, chemically modified polysulfones, andethylene oxide grafted "Nylon-6" are examples of noncellulosicmembranes.

Permselective membranes have been used to replace anions or cations suchas in the sweetening of citrus juice. Typically, a sweetening processuses two anion selective membranes separating the juice from twoalkaline electrolytes. A passage of current through all three chamberscauses hydroxyl anions to pass from one alkaline electrolyte into thejuice to neutralize the acid hydrogen cation while the citrate anionsare passed into the other alkaline electrolyte forming a salt.

Certain biological materials such as proteins are known to besemiconductors with high activation energies inversely proportional toabsorbed water. These biopolymers have a relatively low ionicconduction, i.e., ionic conduction proportional to water absorption.

BRIEF SUMMARY OF THE INVENTION

This invention comprises the discovery that long polymeric chains whichimmobilize water, i.e., absorb and bind or modify water when dispersedin a nonporous matrix, can transport ions provided that: 1) a source ofthe ions exists adjacent to one side and 2) a constant removal of thesame ions occurs on the other side. In the practice of this invention itis assumed that each dispersed polymer, the polymers hereinafter beingreferred to as hydrogels, has an associated chain of water moleculesattached to its length or spine. Each water chain functions as an ionicsemiconductor with a conductance which is low compared to a waterchannel or pore as exists in other polymeric membrane materials. As asemiconductor, materials in accordance of the invention have a highactivation energy of conductance, i.e., an energy well above 5kiloJoules/mol, which makes conductivity very dependent upontemperature. This invention additionally encompasses the discovery thatit is possible to achieve a high density of conductive molecules tothereby obtain conductivity comparable to porous ion exchange membranes.A critical upper density level is found when the hydrogel molecules aredispersed within an inert matrix, this critical level being exhibited bythe development of pores and gelling. If the density is too low, theconductivity of the material becomes too low for most applications sincethe matrix contains no water molecule chains. The invention is able toutilize a polymer such as polyvinylidene chloride which has a low freevolume and has applications because of its low permeability. It shouldbe noted that the chains of water of this invention are different fromthe channels of water in other membranes. The chains of water of thisinvention are bound to the matrix which is of itself nonporous and hencethe water molecules are not free to move as they may in open channels ofwater as occur in porous materials. Since the water molecules in thebound chain are immobilized and thus cannot diffuse, the water chaindoes not function as a pore.

Briefly stated, the invention in a preferred form is an ionicsemi-conductive material which has 10 to 50 percent by weight of a waterabsorbing and bonding long chain molecule (hereinafter called ahydrogel) dispersed within an inert and nonporous matrix. The hydrogeland matrix form a composite wherein there is sufficient bonding betweenthe hydrogel and the matrix so that the composite is inert, there is nosubstantial leach out of the hydrogel, and the quantity of water thatcan be absorbed by the composite does not exceed the weight of thecomposite.

The transport of ions through the composite depends upon thesimultaneous existence of an ion source upon one side and the existenceof an ionic depletion gradient upon the other.

The water bonding material (hydrogel) is preferably selected from thegroup consisting of the synthesized or man-made long chain polymerichydrogels including polyethylene oxide, polyacrylic acid andpolyacrylamide. Hydrogels obtained from natural sources such ashydroxyethyl cellulose, gelatin, pectin, cellulose, and starch may alsobe utilized with a sacrifice in certain operational characteristics. Thebest performance is obtained with high molecular weight andelectrochemical non-ionic hydrogels.

The matrix material is preferably selected from the group consisting ofpolyvinylidene chloride, polyvinylidene dichloride, polyvinyl chloride,polyvinylidene flouride, polyethylene, polypropylene, and polyurethane.A coupling agent may be added to the composite to facilitate the bondingbetween the hydrogel and the matrix. The coupling agent, if employed, ispreferably selected from the group consisting of polyacrylic acid,phenolic resin, cellulosic titanate, carbon, lignin, and silica. Manycommercial plastic resins or latexes are able to bond certain hydrogelswithout added coupling agents.

A method for making a membrane in accordance with the present inventionincludes dispersing a hydrogel in a polymer, i.e., an inert matrixmaterial, which has the necessary physical bulk properties. The weightof the dispersed hydrogel will be in the range of 10 to 50 percent ofthe total weight of the hydrogel-matrix material. The hydrogel andmatrix material are mixed to obtain a substantially uniform distributionof the hydrogel throughout the matrix. The mixture may be formed into asheet or other required geometry. The mixing process typically comprisesthe steps or melt blending and pressure mixing the hydrogel and matrixmaterial. The mixture may be dissolved or dispersed in a solvent anddeposited on a substrate and dried or fused. Water based resins such aslatexes can also be used with thorough mixing of the liquid resin andhydrogel. As noted above, a coupling agent may be added to the hydrogelor to the matrix material to facilitate bonding with the matrixmaterial. Unlike conventional polymeric membranes, the free volumeshould be kept at a minimum.

DESCRIPTION OF THE DRAWING

FIG. 1 is a graph illustrating resistivity, the quality factor and thewater absorption gain for various concentrations in membranes of thepresent invention; and

FIG. 2 is a graph illustrating the current vs. voltage relationship foran electrolyzer cell employing a membrane in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the invention, a membrane or composite material whichmay transport certain ions, and which may exhibit preferential iontransport or water vapor transmission characteristics, results from arestricted concentration of hydrogel, i.e., water modifying polymer,dispersed and confined within an inert matrix which is not of itselfporous. The composite material has 10 to 50 percent by weight ofhydrogel dispersed in the matrix in such a manner that sufficientbonding is provided between the hydrogel molecules and the matrixmaterial to prevent the hydrogel molecules from leaching out and also toprovide a material composite which is inert to the environment. In someapplications, physical intertwining of the matrix and hydrogel moleculesmay furnish sufficient bonding.

It is believed that the invention may best be described and appreciatedby briefly outlining known and/or theorized properties andcharacteristics of a composite material comprising a hydrogel containingnonporous matrix.

In idealized form, such a composite material is theorized to consist ofseparate linear high molecular weight hydrogel chains which are alignedin parallel fashion extending from one surface to the other and arebound within the containing matrix. The hydrogel molecules are singlechain linear polymers with a high degree of hydrophilicity. Eachhydrogel chain is ideally separated (non-crystallized) with otherhydrogel molecules so that excess swelling or gellation does not occurbetween the molecules. When the hydrogel composite is placed in anelectrolyte or a water solution, the hydrogels absorb a limited amountof water with one molecule of water bonding to each active site on thehydrogel polymer.

An idealized model comprises a series of water molecules evenly spacedwith such a close proximity that protons and other ions may freely passalong the spine of the hydrogel chains. (It is not yet known whetherions traverse from bound water sites to bound water sites, or from emptywater sites to empty water sites or whether ions migrate via vacanciesof atoms within the bound water molecules). Each molecule of water issufficiently bound so that the water molecule is not free to move bynormal diffusion, i.e., the water in the sheath essentially assumesice-like characteristics. The hydrogel chains thus serve to provideimmobilized or "frozen" sheaths of bound water molecules. The sheaths ofwater or the water bonding sites and thermal energy are theorized toprovide the mechanism for ion conduction.

The take-up or absorption of water by hydrogels is itself theorized toinvolve sequential ion transfers as opposed to an inflow of freelymoving water molecules as is common with pores or channels.Consequently, it may be assumed that water may permeate the compositematerial as separate hydroxyl and hydrogen atoms and the resultingpermeation of the water throughout the hydrogel material may thus resultfrom ions "hopping" from a filled site to an empty site along a hydrogelchain. This "hopping" phenomenon provides an explanation for thepervaporative properties of the novel hydrogel containing compositematerials of the present invention. The pervaporative properties referto the phenomena wherein, even though water will not pass through the"waterproof" composite materials, the water vapor equilibrium can bemaintained by the drier side of the hydrogel material evaporating waterwhile the wetter side of the composite material supplies replacementwater ions, i.e., the materials of the present invention are"breathable".

Ion transport through hydrogel containing composite materials inaccordance with the invention is theorized to proceed in a manneranalogous to the take up of water by the hydrogel chains with ions"hopping" from water molecule to water molecule or from a donor site toan acceptor site in a manner analogous to the conventional protontransport theory for ice and other proton conductive materials. It is ofcourse possible that there are active sites on the hydrogel chain whichfunction as do the hypothesized water sites. The process of iontransport involves a transfer of energy from an acceptor site to atrapped ion. The energy for such transfers is supplied by thermal energywhich is demonstrated by the high temperature coefficients or activationenergies of the materials of this invention. The ion conduction processis properly characterized as a facilitated carrier process rather thanthe previously known solubilization and channel conduction process whichoccurs in conventional permselective membranes.

An unexpected property of the membranes of this invention is that ionsare not transmitted through the membrane if only a concentration,pressure, or voltage gradient exists across the membrane. If fluids ofdifferent heights or ionic concentration or with a voltage gradientwithout a current flow exist across the membrane, no ion transportoccurs because of these conditions alone as is common with commercialmembranes.

If two ionic mixtures are separated by the membranes of this invention,no ion transfer (no diffusion) will take place as long as theelectrolytes are each at equilibrium. Under ideal conditions, it isassumed that ions can move along the hydrogel chains and form electricaldouble layers at the membrane/electrolyte interfaces to balance thechemical potential. This is similar to the migration of holes andelectrons in an electronic semiconductor under an external field to forma potential barrier at a junction. This potential barrier is stable withtime and charges can flow through the material only if an equal numberof charges are being removed from one of the interfaces to provide"holes" to which the ions may "jump". The ion transfer process isbelieved to require both the availability of ions on one side of themembrane and the removal of ions on the other side. The inner chargetransfer of the membrane is therefore coupled with the external ionicelectrochemical depletion gradient and therefore to the electrodereactions in an electrochemical cell. Selectivity of the membrane, i.e.,the preferred ion transfer, thus appears not to be determined so much bythe membrane characteristics, but by the electrode/electrolyte reactionsor surface ionic concentration gradient variations.

The ion which is transferred through the membrane may not be the ionoxidized or reduced at an electrode since the ion reaction at theelectrode may in turn react with or be the result of another reaction inthe electrolyte which in turn causes the increase or decrease in theactivity or concentration of another ion at the surface of the membrane.

Under ideal conditions, as discussed above, a single chain of water isassumed to exist along which ions can pass by "hopping" from watermolecule to water molecule. It is assumed that the surrounding matrixcontains no charges or can not interact in any manner with the transferof ions. Under these ideal conditions, it can be expected that therewill be a velocity difference between different ions since differentenergies will be required for them to "hop". Experiments demonstratethat the ions do in fact have relative velocities corresponding closelyto their relative velocities at infinite dilution in water. That is,protons will be transported at about 6 times the velocity of copperions, (H+=340 mho-cm² /equivalent and Cu++=55 mho-cm² /equivalent fortheir limiting equivalent conductance at infinite dilution). Thisproperty allows usage of the membranes of the invention in chemicalseparations.

An unexpected characteristic of the composite materials of the presentinvention, and thus of the theorized ionic conduction process, residesin the fact that the ionic conduction through the material does notrequire the presence of an inner electric field and the matrix can bemade electrically conductive without limitation of the conductionprocess. This is contrary to the normal considerations for membranes.Further, the ionic conductance of the material is not highly dependentupon the thickness of the material as is normal for most conductivematerials. The transfer of ions in the material is highly dependent uponthermal energy which supplies the transfer energy as well as emptyreceptor sites in the adjacent water molecules or acceptor sites on thechain. It is the requirement for both heat and an empty "hole" inaddition to a source of ions in order for an ion to move whichcharacterizes the operation of the materials. For holes to continuouslyexist, there must be a continuous removal of ions from the surface ofthe membrane, i.e., an ion depletion gradient must exist. This in turnrequires that ions be continuously removed from the electrolyte whichrelates the inner transfer of ions to the reactions within theelectrolytes rather than to concentration differences or pressure.

Under less than ideal conditions, i.e., when working with materialswhich can be practically manufactured, the molecules of the hydrogelmaterial do not align in a perfectly parallel orientation nor are thehydrogel molecules uniformly spaced throughout the matrix. Under suchreal world conditions, the orientations of the hydrogel molecules tendto approach more of a "can of worms" model. At a threshold densitylevel, if the density of the hydrogel molecules is decreased, conductivepaths through the matrix theoretically decrease since single polymericchains are no longer continuous from one side of the hydrogel materialto the other side and isolated chains of hydrogel molecules are not incontact with either a surface of the hydrogel material or other chainsfor ion transference. With increasing density of hydrogel molecules, theadjoining of hydrogels or crystallization can take place with noseparating matrix. At such crystallization sites, large channels ofwater may form many molecules deep or water or electrolyte may beabsorbed at the sites but not be tightly bound. These latter areas ofjoined hydrogels without a retaining matrix may display thecharacteristics of a normal dissolved or gelled hydrogel with a largewater absorption but without selective ion conductance. The areas ofjoined hydrogel molecules are believed to function as do the centersformed by grafted or added active ion centers of conventional ionexchange materials.

In accordance with the invention, the hydrogel/matrix composite may,depending upon the hydrogel density, function as a composite materialhaving a low ionic conductance which approaches that of the matrixmaterial (if the hydrogel content is too low) or a material with a veryhigh water content which behaves as a gel with high diffusion (if thehydrogel concentration is too high).

The effect of encapsulating the individual hydrogel (HYD) molecules andlimiting the water absorption of the hydrogel/matrix composite can beascertained from Table 1. Table 1 illustrates a comparison of thehydrogel concentration before (dry) and after (wet) soaking thehydrogel/matrix composite in water. The hydrogel concentration isexpressed as a weight percent of the total hydrogel/matrix compositematerial for four different hydrogel concentrations. In the examplesfrom which the Table 1 data was collected, the hydrogel was polyethyleneoxide (WSR-301 Polyox, Union Carbide Corporation) and the matrixmaterial was a phenolic resin (12704 Phenolic resin phenol formaldehyde,Durez Division of Hooker Chemical Corporation).

                  TABLE 1                                                         ______________________________________                                        wgt % of HYD (dry)                                                                             67    60        50  44                                       wgt % of HYD (wet)                                                                              2     6        33  36                                       water gain (times)                                                                             27    10         1  0.5                                      H.sup.2 O/HYD (wet)                                                                            40    17         2  1                                        ______________________________________                                    

As can be determined from Table 1, the ratio of the absorbed water tothe initial weight increases exponentially with increasing initialpercentage of hydrogel. This characteristic may be explained by theincreasing numbers of associated hydrogel molecules which are capable ofmaintaining a channel of water between them as well as by the weakeningof the restraining structure of the surrounding matrix.

Table 2 provides a comparison of membrane resistivity (rho=Ohm-cm²), andthe electropermeability of copper (P=micrograms per membrane voltagedrop-cm² -hour), versus the dry percentage weight of hydrogel in thehydrogel/matrix composite (% HYD) and the percentage gain in weight ofthe composite after soaking in water. In the examples from which thedata of Table 2 was collected, the hydrogel material (HYD) ispolyethylene oxide (WSR-301 Polyox, Union Carbide Corporation) and thematrix material is polyvinylidene chloride (864 "Saran" resin, DowChemical Corporation). The test cell was a Pt/H² SO₄ /CuSO₄ /Cu coupledriven with a constant current operated for two hours with the copperelectrode negative. The expected reactions can be written as: ##STR1##where the electrochemically formed protons are transferred through themembrane as indicated by the dashed line and the electrons aretransferred by the external circuit indicated by a solid line. A secondreaction can also take place, which is the normal copper platingequation: ##STR2## where the Cu++ ion is transferred through themembrane and plates on the cathode. This reaction competes with thefirst reaction and is reduced by complexing of copper ions in theanolyte and an increase in the H₂ SO₄ /CuSO₄ ratio. If a membraneobtains equilibrium water uptake and is then suddenly used as a membranein the above cell, a time factor becomes manifest, since it takes timefor the copper ions to traverse the already saturated water chains. Thetime for an equilibrium output of copper/proton ion ratio in thecatholyte will depend upon the current density, the thickness of themembrane and the number of hops along the chain. Any increase in theamount of copper over 16% of the total current after equilibrium andwith low copper complexing has been found to be indicative of pore orchannel formation. The resistivity, however, will depend upon the numberof chains. Membranes can be evaluated therefore by comparing resistivityand the electropermeation of copper at constant current over a fixedtime interval. Low copper transfer and low resistivity are indicative ofbetter membranes according to this invention.

                  TABLE 2                                                         ______________________________________                                        % HYD     % GAIN (H.sub.2 O)                                                                         rho      P        Q                                    ______________________________________                                        12        11           131      51       150                                  20        24           35       6        5100                                 30        47           9.6      280      370                                  40        87           0.3      60,000   60                                   ______________________________________                                    

As can be determined from Table 2, the resistivity is an inverseexponential function of the percentage of hydrogel as expected. Theelectropermeation of copper increases with the increasing percentage ofthe hydrogel presumably because of the increasing numbers of associatedhydrogel molecules which can form gelled water channels. The decreasesin the electropermeation from the 12 percent concentration to the 20percent concentration can be explained by the rapid decrease inresistivity and hence the decrease in the membrane voltage drop as thehydrogel content decreases.

FIG. 1 is a composite graphical representation of the data of Table 1and Table 2. Curve 10 illustrates the resistivity data of Table 2. Curve20 illustrates the water gain data of Table 1. The curve 30 is asmoothed curve representing the quality factor data of Table 2. Thecriticality of the Q curve is quite evident. It should also beappreciated from FIG. 1 that the percentage of hydrogel used for a givenapplication is dependent upon the compromising of the actual operatingcharacteristics which are desired. For instance, if low diffusion is ofprime importance, then the percentage of hydrogel used will be lowerthan if a low resistivity is of prime importance. The actual measuredcharacteristics as set forth in Tables 1 and 2 depend upon the specifichydrogel. Some hydrogel materials and the associated water willnaturally be better conductors of the ion of interest than othersbecause of better site to site spacing along the chains.

FIG. 1 is, however, generally exemplary of graphical representations ofthe properties of hydrogel materials in an inert resin matrix inaccordance with the present invention. Curves derived for othercombinations of hydrogels and matrices can be expected to deviate onlyslightly with respect to abscissa coordinates and quite strongly withrespect to the ordinate coordinates.

Membranes in accordance with the present invention are formed from twobasic components, the hydrogel and the matrix. The hydrogel materialmust be dispersible throughout the matrix. Sufficient bonding betweenthe hydrogel and the matrix is required to prevent leaching of thehydrogel. The matrix must also exhibit mechanical properties sufficientfor the end usage. Conductive particles, such as carbon or metal powder,or fibers can be added to the hydrogel material to reduce the innerelectrical field or to provide electron conductance through thematerial.

Electrochemically active and other materials may also be added to thecomposite. For instance, special polymeric electrodes can be formed bycombining an active electrode material such as zinc, silver oxide, M_(n)O₂, or lead with the composite containing an electron conductivematerial. Such electrodes operate by conducting the exchange electronsthrough the electron conduction portion of the composite and theexchange ions through the water chains.

The composite materials of the invention may be prepared by using eithera dry mix or a liquid mix. The liquid mixes are used primarily in theapplication of a coating to a substrate or in the fabrication of verythin membranes. The dry mixes are prepared by state of the arttechniques for the production of polymeric alloys. The principal problemwhich is ordinarily encountered in alloying polymers is the obtaining ofsufficient bonding between the two materials. The mixing rate, shearforces, temperature and time are all factors in obtaining positivebonding characteristics. Coupling agents can be added to facilitate thebonding and many commercial suppliers of resins add coupling agents,plasticizers, anti-oxidants, etc., which may serve to assist in thebinding of hydrogels. Materials such as silica and carbon have beensuccessfully employed as coupling agents. Another technique employed tofacilitate the bonding is to first associate two hydrogels together orto insolubilize a hydrogel to produce a less active hydrogel moleculebut one which has better bonding characteristics with the matrixmaterial.

The ratio of hydrogel to the matrix may be varied to yield materialshaving a wide range of properties. In general, composites having a lowratio of hydrogel to matrix material result in a low ionic permeationwith near zero diffusion, low swelling (water absorption), limitedsurface activity and very favorable mechanical characteristics of thecomposite. In the case of composites having a high hydrogel material tomatrix material ratio, high swelling (water absorption), high surfaceactivity, high ionic conductivity, increased diffusion due to channelformation and unique physical characteristics are obtained. Thematerials forming the composite membranes may be compounded bystate-of-the-art techniques including dry or melt blending or solventdispersion and mixing. Normal precautions must be taken to prevent overor under mixing which results in either excessive molecular weightreduction through chain breakage or in low dispersion and poorassociation. Care must also be taken with time-temperature cycles toavoid excessive oxidation or thermal degradation.

For Examples 1-8 and 12-19, below, sheets or solid thick films of thehydrogel materials were prepared by weighing and mixing the dryingredients and then blending the ingredients in a two roll chemicalmill or in a heated press. The mixing in the mill was in accordance withnormal usage. A laboratory press was found satisfactory for preparingsmall sample lots. The mixed, weighed samples were melt blended betweentwo flat plates using conventional mold release agents to preventadhesion. The temperature was adjusted to compromise the thermaldegradation with the viscosity and ease of mixing as common to the art.Pressure was applied to force the shearing flow of the melt between theplates and, hence, the mixing of the matrix and hydrogel materials. Thepress and the plates were then opened and the pressed sheet was foldedor formed into a compact mass and then repressed. This latter procedurewas continued until the materials were uniformly mixed. The finalpressing yielded flat sheets which were then cut to size for testingpurposes. The thickness of the formed sheets of composite was typicallybetween 0.02 and 0.03 cm (in thickness). Other methods of mixing such asextrusion, heat blending and pelletizing may also be used to form thecomposite material.

For Examples 9-12, below, liquid mixes were prepared by state-of-the-arttechniques. The hydrogels were usually first dispersed in an organicsolvent in which the hydrogel is not soluble. The matrix and additivesfor further mixing were added to the hydrogel and solvent. Water wasthen slowly added during the mixing process. The viscosity and flowcharacteristics of the resulting solution were controlled to some degreeby the amounts of the solvent and the added water. Once the mixing wascomplete, the mixture was applied to a substrate or cast into films byknown methods. The film or coating was then allowed to dry and was bakedor cured depending upon recommendations from the manufacturers of theingredients. In general, lower temperatures and longer times of bakingor curing are preferred instead of short times at high temperatures.

The membranes of the present invention differ from previous hydrogelmaterial composites in the dispersion of critical quantities of hydrogelin the final water swollen state in an inert and nonporous matrix. Thedispersion of separated hydrogel molecules minimizes crystallization orhydrogel to hydrogel association and hence decreases channel formationand water absorption. The present invention avoids the formation of agel or intercoupling of hydrogel molecules whereas past usage desiredthe gelation of hydrogels.

An inert matrix functions to separate and restrain the hydrogelmolecules and consequently there is substantially less swelling orweight gain due to the absorption of water by the formed material. Inaccordance with the invention, the proportion of hydrogels employed isin the range of between 10 and approximately 50 percent by weight of thedry composite. The proportion may be further limited for melt-mix andsolvent based systems which require a ration from about 20 to 50% andfor water based systems which require about a 10 to 40 percent ratio ofhydrogel to matrix. This results in a composite material which does notabsorb sufficient water to double the weight of a formed membrane.General limitations may also be placed upon the selected hydrogels orwater modifiers used as constituents in the membrane. A first limitationis the compatibility of the hydrogel with a given matrix material. Asecond limitation is the stability of the hydrogel both mechanically andchemically at the temperature of operation for the membrane. A thirdlimitation is the conductivity of the hydrogel/water, particularly whenion transfer is of primary importance. A fourth limitation is that thehydrogel must have sufficient molecular weight or be of such a lengththat the number of hydrogel molecules necessary to connect one side of amembrane to the other are minimized.

The following examples are given for purposes of illustration only inorder that the invention may be more fully understood. The examples arenot intended to in any manner limit the practice or scope of theinvention. Unless otherwise specified, all (specified) proportions aregiven by weight.

EXAMPLE 1

A sheet of material was prepared from 12 percent Union CarbideCorporation 4,000,000 molecular weight polyethylene oxide sold under thetrade name "Polyox 301" and 88 percent Dow Chemical Corporationpolyvinylidene chloride sold under the trade name "Saran 864 resin". Themixture was heat blended and pressure mixed in a press as previouslydescribed to form flat sheets of material. The formed sheets wereweighed and then soaked in water at room temperature for at least twohours. The sheets were blotted dry and reweighed. The absorbed water wasfound to increase the weight of the sheets by 11 percent.

EXAMPLE 2

A sheet of material was prepared from 20 percent Union CarbideCorporation 4,000,000 molecular weight polyethylene oxide sold under thetrade name "Polyox 301" and 80 percent Dow Chemical Corporationpolyvinylidene chloride sold under the trade name "Saran 864 resin". Theforegoing materials were mixed, heat blended and pressure mixed in apress as previously described to form flat sheets of material. Theformed sheets were weighed and soaked in water at room temperature forat least two hours. The sheets were blotted dry and reweighed. Theabsorbed water was found to increase the weight of the sheets by 24percent.

EXAMPLE 3

A sheet of material was prepared from 15 percent B. F. Goodrich Co.3,000,000 molecular weight polyacrylic acid sold under the trade name"Carbopol 934", 15 percent Union Carbide Corp. 4,000,000 molecularweight polyethylene oxide sold under the trade name "Polyox 301", and 70percent Kay-Fries, Inc. polyvinylidene fluoride sold under the tradename "Dyflor 2000". The polyacrylic acid was mixed with the polyethyleneoxide to insolubilize the polyethylene oxide and to facilitate bondingto the polyvinylidene fluoride matrix. The polyacrylic acid is also ahydrogel. The foregoing materials were mixed, melt blended, and pressuremixed in a press as previously described to form flat sheets ofmaterial. The sheets were weighed and then soaked in water at roomtemperature for at least two hours. The sheets were blotted dry andreweighed. The absorbed water was found to increase the weight of thesheets by 16 percent.

EXAMPLE 4

A sheet of material was prepared from 20 percent B. F. Goodrich Co.3,000,000 molecular weight polyacrylic acid sold under the trade name"Carbopol 934", 20 percent Union Carbide Corporation 4,000,000 molecularweight polyethylene oxide sold under the trade name "Polyox 301", and 60percent Kay-Fries, Inc. polyvinylidene flouride sold under the tradename "Dyflor 2000". The polyacrylic acid was mixed with the polyethyleneoxide to insolubilize the polyethylene oxide and to facilitate bondingto the polyvinylidene fluoride matrix. The polyacrylic acid is also ahydrogel. The foregoing materials were mixed, melt blended, and pressuremixed in a press as previously described to form flat sheets ofmaterial. The sheets were weighed and then soaked in water at roomtemperature for at least two hours. The sheets were blotted dry andreweighed. The absorbed water was found to increase the weight of thesheets by 33 percent.

EXAMPLE 5

A sheet of material was prepared from 25 percent B. F. Goodrich Company3,000,000 molecular weight polyacrylic acid sold under the trade name"Carbopol 934", 20 percent Union Carbide Corporation 4,000,000 molecularweight polyethylene oxide sold under the trade name "Polyox 301", and 55percent Kay-Fries, Inc. polyvinylidene fluoride sold under the name"Dyflor 2000". The polyacrylic acid was mixed with the polyethyleneoxide to insolubilize the polyethylene oxide and to facilitate bondingto the polyvinylidene fluoride matrix. The polyacrylic acid is also ahydrogel. The foregoing materials were mixed, melt blended, and pressuremixed in a press as previously described to form flat sheets ofmaterial. The sheets were weighed and then soaked in water at roomtemperature for at least two hours. The sheets were blotted dry andreweighed. The absorbed water was found to increase the weight of thesheets by 42 percent.

EXAMPLE 6

A sheet of material was prepared from 50 percent B. F. GoodrichCorporation 3,000,000 molecular weight polyacrylic acid sold under thetrade name "Carbopol 934" and 50 percent Borden Company homopolymerpolyvinyl chloride resin sold under the trade name "VC-54". 0.025%neoalkoxy titanate sold by Kenrich Petrochemicals, Inc. under thedesignation "LICA 12" was added to facilitate the bonding of thehydrogel to the matrix. The foregoing materials were mixed, meltblended, and pressure mixed in a press as previously described to formflat sheets of material. The sheets were weighed and then soaked inwater for at least two hours. The sheets were blotted dry and reweighed.The absorbed water was found to increase the weight of the sheets by 76percent.

EXAMPLE 7

A sheet of material was prepared from 25 percent Union CarbideCorporation hydroxyethyl cellulose sold under the trade name "CellosizeQP 4400 H", 25 percent polymerizable cellulosic sold under thedesignation "105" by A. E. Staley Manufacturing Company, and 50 percentBorden Company homopolymer polyvinyl chloride resin sold under the tradename "VC-54". The cellulosic was added to facilitate the bonding of thehydrogel to the matrix. The cellulosic may also partially function as ahydrogel. The foregiong materials were mixed, melt blended, and pressuremixed as previously described to form flat sheets of material. Thesheets were weighed and then soaked in water at room temperature for atleast two hours. The sheets were blotted dry and reweighed. The absorbedwater was found to increase the weight of the sheets by 41 percent.

EXAMPLE 8

A sheet of material was prepared from 40 percent pectin, 10 percentpolymerizable cellulosic sold under the designation "106" sold by A. E.Staley Manufacturing Company, and 50 percent Borden Company homopolymerpolyvinyl chloride resin sold under the trade name "VC-54". Thecellulosic was added to facilitate the bonding of the hydrogel to thematrix. The cellulosic may also partially function as a hydrogel. Theforegoing materials were mixed, melt blended, and pressure mixed aspreviously described to form flat sheets of material. The sheets wereweighed and then soaked in water at room temperature for at least twohours. The sheets were blotted dry and reweighed. The absorbed water wasfound to increase the weight of the sheets by 13 percent.

EXAMPLE 9

A coating was prepared from 20 percent Union Carbide Corp. 4,000,000molecular weight polyethylene oxide sold under the trade name "Polyox301" and 80 percent Durez phenol formaldehyde sold under the trade name"12704 Phenolic resin". The foregoing materials were mixed and water wasadded to the mixture during the mixing process. The coating was appliedto a commercial grade of Kraft paper. The coating was allowed to dry andwas treated as previously described.

EXAMPLE 10

A first coating was prepared from 33 percent Union Carbide Corp.hydroxyethyl cellulose sold under the trade name "Cellosize QP 4400 H"and 67 percent Durez phenol formaldehyde sold under the trade name"12704 Phenolic resin". The foregoing were mixed and water was added tothe mixture during the mixing process. A second coating was preparedfrom 33 percent B. F. Goodrich Co. 3,000,000 molecular 934" and 67percent Durez phenol formaldehyde sold under the trade name "12704Phenolic resin". The foregoing materials were mixed and water was addedto the mixture during the mixing process. The first coating was appliedto one side of a commercial grade of Kraft paper and the second coatingwas applied to the other side of the Kraft paper. The coatings wereallowed to dry and were cured as previously described.

EXAMPLE 11

A coating was prepared from 9.7 percent Union Carbide Corp. 4,000,000molecular weight polyethylene oxide sold under the trade name "Polyox301", 58.3 percent Dow Chemical Corp. copolymer of vinylidene chlorideand others sold under the trade name "RAP 184 Latex", and 2 percent B.F. Goodrich Co. 3,000,000 molecular weight polyacrylic acid sold underthe trade name "Carbopol 934". The polyacrylic acid was added to thepolyvinylidene chloride to insolubilize the polyethylene oxide andfacilitate the bonding. The foregoing materials were mixed and water wasadded to the mixture during the mixing process. The coating was appliedto a commercial grade of Kraft paper. The coating was allowed to dry andwas baked as previously described.

EXAMPLE 12

A coating was prepared from 20 percent Union Carbide Corp. hydroxyethylcellulose sold under the trade name "Cellosize QP 4400 H" and 80 percentLoctite Corp. two part expoxy sold under the trade name "EPOXE". Theforegoing materials were mixed and water was added to the mixture duringthe mixing process. The coating was applied to a commercial grade ofKraft paper. The coating was allowed to dry and to cure.

EXAMPLE 13

A sheet of material was prepared from 30.8 percent Union Carbide Corp.4,000,000 molecular weight polyethylene oxide sold under the trade name"Polyox 301", 56.8 percent polypropylene resin sold under the trade name"Pro-fax PC072" by Himont U.S.A., Inc., 10 percent Cabot Corporationfumed silica sold under the trade name "Cab-O-Sil EH-5", and 12.4percent phenol formaldehyde sold under the trade name "Durez 12704Phenolic resin" by Hooker Chemical Corporation. The poly-propylene resinand silica were premixed to facilitate bonding with the polyethyleneoxide and phenolic. After pre-mixing, the foregoing materials weremixed, melt blended, and pressure mixed as previously described to formflat sheets of material. The sheets were weighed and then soaked inwater at room temperature for at least two hours. The sheets wereblotted dry and reweighed. The absorbed water was found to increase theweight of the sheets by 50 percent.

EXAMPLE 14

A sheet of material was prepared from 50 percent Allied ChemicalCorporation polyacrylamide flocculent sold under the trade name "A210"and 50 percent polypropylene resin sold under the trade name "Pro-faxPC072" by Himont U.S.A., Inc. The foregoing materials were mixed, meltblended, and pressure mixed as previously described to form flat sheetsof material. The sheets were weighed and then soaked in water at roomtemperature for at least two hours. The sheets were blotted dry andreweighed. The absorbed water was found to increase the weight of thesheets by 38 percent.

EXAMPLE 15

A sheet of material was prepared from 30 percent starch derivative soldunder the tradename "SGP 147" by Henkel Corporation, and 70 percentBorden Company homopolymer polyvinyl chloride resin sold under the tradename "VC-54". The foregoing materials were mixed, melt blended, andpressure mixed as previously described to form flat sheets of material.The sheets were weighed and then soaked in water at room temperature forat least two hours. The sheets were blotted dry and reweighed. Theabsorbed water was found to increase the weight of the sheets by 11percent.

EXAMPLE 16

A formulation was prepared from 33% cellulose fibers prepared from Kraftpaper by soaking the paper in a heated sodium hydroxide solution, thenwashing, filtering and drying. The fibers contain natural hydrogelchains extending along their lengths. The fibers were dispersed in apolyvinylidene fluoride resin sold as "Floraflon 1000 LD" by UgineKuhlman of America, Inc. The foregoing materials were melt-mixed andextruded to form flat sheets of material. The sheets had a highresistivity of 600 Ohm-cm².

EXAMPLE 17

A two-stage formulation was prepared from 50% silica as Cab-O-Sil*(Cabot Corp. M-5 dispersed in cellosolve), 50% Gelatin USP (KnoxGelatine, Inc.) dissolved in water. The foregoing materials were mixedin a blender, spread out on a surface, and dried. Fifty percent (50%) ofthe foregoing dried mixture was combined with 50% polyvinylidenefluoride as Florafon* 1000 LD (Ugine Kuhlman of America, Inc.). Thematerials were melted, mixed and extruded to form a flat sheet of about0.1 cm thickness with an activation energy of conduction over 10kiloJoules/mol.

EXAMPLE 18

A sheet of material was prepared from 70 percent of a commercialpolyethylene electrically conductive resin containing about 20 percentactivated carbon supplied by Modern Dispersions, Inc. sold under thelabel of "PM 530"; 25 percent Union Carbide Corporation 4,000,000molecular weight of polyethylene oxide sold under the trade name "Polyox301"; and 5 percent of a modified ethylene vinyl alcohol adhesivesupplied by Chemplex Company sold under the trade name of "Plexar 100".The "Plexar 100" was added to facilitate alloying the mixture. Thematerials were melt blended and pressure mixed as previously describedto form flat sheets of material. The sheets were weighed and then soakedin water for at least two hours. The sheets were blotted dry andreweighed. The absorbed water was found to increase the weight of thesheets by 27 percent.

EXAMPLE 19

A sheet of material was prepared from a melt blend of 20 percent UnionCarbide Corporation 4,000,000 molecular weight polyethylene oxide soldunder the trade name "Polyox 301"; 20 percent activated carbon powdersold under the trade name "Vulcan XC 72R" by Cabot; and 60 percentpolypropylene resin sold under the trade name "Pro-Fax PC072". The meltpressed sheets were soaked in water for at least two hours. The absorbedwater was found to increase the weight of the sheets by 12.2 percent.

Various measurements and properties of the membranes, i.e., the sheetsand coated materials, of Examples 1 through 19 are summarized and setforth in TABLE 3 below. Example R is a commercially availablepermselective membrane composed of perfluorosulfonic acid which is soldby DuPont under the trade name "Nafion 125". Example R is a referencematerial included for purposes of comparison.

                  TABLE 3                                                         ______________________________________                                        Example % Hydrogel % H.sup.2 O                                                                            Rho   P      Q                                    ______________________________________                                         1      12         11       130   50     150                                   2      20         24       35    6      4800                                  3      15         16       67    187    67                                    4      20         33       26    40     1040                                  5      25         42       11    30     2900                                  6      50         76       190   81     65                                    7      25         41       40    625    40                                    8      40         13       78    156    80                                    9      20                  190   76     69                                   10      33                  170   17     340                                  11      10                  160   196    31                                   12      20                  64    190    79                                   13      31         50       50    450    44                                   14      50         38       92    33     326                                  15      30         11       200   340    15                                   16      33                  600   235    7                                    17      25                  2000  20     25                                    8*     25         27       0     NA     NA                                    19**   20         12       0     NA     NA                                   R                   9       1     86000  19                                   ______________________________________                                         *Example 18 was constructed of an electron conducting membrane and hence      the measured voltage drop across the membrane was zero. The amount of         copper which permeated the membrane equalled an equivalence to less than      2.7 percent of the total current.                                              **Example 19 was electron conducting and had a copper permeation less        than a 1.5 percent equivalence to the current with a small amount of          copper plating found at the interface of air, copper electrolyte and          membrane continuing a few millimeters on the membrane air interface.     

The water absorption measurements (% H₂ O) of Table 3 are a sensitivetest of the materials due to the strong affinity of the hydrogels forwater. Prepared samples were weighed and placed in water at a roomtemperature and allowed to soak for at least four hours. The sampleswere then blotted dry and reweighed. The gain in the weight was dividedby the original dry weight and multiplied by 100 to yield the percentageof water absorption gain.

The resistivity values (Rho) for Table 3 were first obtained by soakingthe membrane in water to fully absorb the water and then placing themembrane in an electrochemical cell separating two electrolytes. A knowncurrent was passed through the cell and membrane and the voltage dropacross the membrane was measured with a small platinum probe afterinitial polarization was reached. The resistance of the membrane wasobtained by determining the ratio of the voltage drop to the magnitudeof the electric current. The resistivity (Ohm-cm²) was obtained bymultiplying the resistance by the area of the membrane exposed to thecurrent flow. The resistivity values were determined at roomtemperature. Equilibrium direct current measurements were employed. Theresistance values so obtained are not absolute since an emf existsacross the membrane proportional to the difference in chemical potentialexisting between the two electrolytes. In most tests this potentialincreases with time because of the potential in pH which take place witha current flow.

The electrical permeation (P) for Table 3 is indicative of the passageof copper ion through the membranes under the electrochemical ionicgradient. A high percentage of permeation indicates the formation ofpores or open channels of water. The membrane to be tested was placed inan electrochemical cell separating an acid copper plating solution (20%wgt CuSO₄. 6% H₂ SO₄) as the anolyte and a 10% H₂ SO₄ solution as thecatholyte. A copper anode was used with a weighed platinum cathode. Aknown current with a density of about 6 mA/cm² was passed through themembrane for two hours. The copper ions which permeated through themembrane were plated out on the platinum cathode. The platinum cathodewas weighed to determine the quantity of plated copper. During the test,the voltage drop across the membrane was measured with a platinum probe.The final electropermeation co-efficient was obtained by dividing theweight in micrograms of the copper plated on the cathode by the productof the membrane voltage drop, the effective area of the membrane and thetime of the application of the electric field. The resultingelectropermeation P is expressed in micrograms per (volt-cm² -hour).

The measured permeation values may be slightly higher than the actualvalues because of surface conductance over the outer edges of themembrane in addition to the transfer through the membrane. This issignificant because of the high surface conductivity of the materials.The measured values may also be slightly lowered due to the observableloss of salts through piezodialysis, such salts appearing on the outeredges of the membrane and outside the cell.

The quality factor (Q) of Table 3 was determined by two operationalfactors, e.g., the ease of permeation of the desired ions and therejection of the undesired ions. The quality factor Q is defined as 10⁶/(rho×P) where rho is the resistivity and P is the electropermeabilityas defined above.

The membranes of Examples 1 through 19 may find applications in manyfields including hydrogen and chlorine generation, batteries,pervaporative films and materials for moisture control, biologicalapplications, pH control, separations, metrology, fuel cells,electrochemical synthesis, and water purification.

The coated paper membrane of Example 11 above was taped to the openingof a 125 ml flask half filled with water kept at 100 degrees F. and itsweight compared over time with a similar filled flask at 100° F. with nocover over the opening. The membrane covered flask demonstrated half theloss of water per hour as did the open flask indicating that themembrane had an equivalent aperture of one half the uncovered flask orfunctioned as if it were 50% porous. This experiment demonstrated thepervaporative properties of the membranes of this invention, in that theflask covered with the membrane could be inverted without any waterleaking through the membrane (waterproof) and yet would pass water vaporto the drier external air (45% relative humidity) at a rate equal to onehalf that of an open flask (breathable).

As noted above, a very early Daniell cell used animal bladders orceramics to keep zinc and copper ions separate. The cell may bedesignated as follows: Zn/ZnSO₄ //CuSO₄ /Cu, where the // designates amembrane without diffusion. As the cell discharges, the zinc reacts withthe acid and the copper sulfate reacts as set forth below: ##STR3## Theanode reactions proceed to the right with the electrons flowing throughthe external circuit and the protons flowing through the membrane. Thecathode reaction proceeds to the left with copper being deposited uponthe cathode. Upon charging the cell the process is reversed, the copperdissolves, the proton flow is reversed and the zinc plates onto the zincelectrode.

The lack of commercial utility of the early Daniell cell resulted fromdeficiencies in the membrane. The animal membranes which were employedhad a relatively short life in the caustic solutions and the alternativeceramic membranes were bulky, fragile and unable to keep the twoelectrolytes from mixing over prolonged periods of time. Copper and zincwould still be the choice for battery materials today since the metalsare both relatively light with a high electrical charge with atheoretical capacity six times the capacity per pound of lead acid andNi/Cad batteries. Further, both metals are in abundance, inexpensive,relatively non-toxic and non-hazardous.

Copper and zinc have problems, however, which have precluded their usagein rechargeable batteries. Zinc when used as an anode fails to replateor reform to its original shape when recharged and tends to grow verythin conductive whiskers or dendrites which can short out the electrodesin just a few recharge cycles. Copper is sufficiently soluble and mobilein most electrolytes to poison the other electrode and electrolyte,gradually dropping the battery performance. Zinc is used in short livedhigh energy per pound batteries with sacrificial wrapping around thezinc to prevent the formation of dendrites. Copper is not used atpresent in any commercial batteries.

EXAMPLE 20

To demonstrate the present invention, a Daniell cell was assembled whichemployed a strip of copper in an acid copper sulfate plating catholyteand a strip of zinc in an ammonium/zinc chloride anolyte. Theelectrolytes were separated by a membrane constructed of 6% silica, 25%Union Carbide Corporation 4,000,000 molecular weight polyethylene oxidesold under the trade name "Polyox 301", 57% polypropylene resin soldunder the trade name "Pro-fax PC072" by Himont U.S.A., Inc., 12 percentphenol formaldehyde sold under the trade name "Durez 12704 Phenolicresin" by Hooker Chemical Corporation. The cell delivered an opencircuit voltage of slightly over one volt with an internal resistance ofabout 40 Ohm-cm² at a current density of about 0.01 Amperes/cm².

EXAMPLE 21

A further Daniell cell was constructed by exchanging the anolyte of theabove example with a 1N KOH electrolyte. The cell open circuit voltagerose to over 1.3 volts and the internal resistance decreased to about 16Ohm cm² at about 0.015 Amperes/cm².

EXAMPLE 22

A further modification of the Daniell cell was tested using copper oxideas the catholyte in a mixture of silica and carbon. Equal volumes ofmicronized amorphous silica sold as IMSIL* A-10 by Illinois MineralsCompany and commercial red copper oxide powder were mixed and placed onthe catholyte compartment and moistened with 1N H₂ SO₄. A membraneconstructed from 16% Union Carbide Corporation 4,000,000 molecularweight polyethylene oxide sold under the trade name "Polyox 301"; 8percent activated carbon powder sold under the trade name "Vulcan XC72R" by Cabot; 10 percent 1/4 inch unsized carbon fibers sold asFortafil* 3 supplied by Great Lakes Carbon Corporation; and 66 percentDow Chemical Corporation polyvinylidene chloride sold under the tradename "Saran 864 resin" separated the catholyte from the abovezinc/anolyte. The cell had an open circuit voltage of about 1.3 voltswith an internal resistance of about 20 Ohms cm² when run at about 0.015Amperes/cm².

Each of the above zinc/copper cells was rechargeable, limited by themorphology of the zinc which deteriorated during each recharging cycle.

EXAMPLE 23

The life of the zinc electrode of the above described cells may beextended without decreasing the performance of the cell by encapsulatingzinc metal in the ionic conducting composite material of this inventionmade electronically conductive by adding carbon or metal particles. Forexample, a composite zinc electrode was constructed of 9% acrylic acidof molecular weight of about 4,000,000 (Carbopol 940, a product of B. F.Goodrich Company); 2.5% carbon powder (Vulcan XC-72, manufactured byCabot Corporation); 4.5% unsized 1/4 inch carbon fibers (Fortafil 3,supplied by Great Lakes Carbon Corporation), 5.3% polypropylene (Pro-faxPC072, manufactured by Himont U.S.A., Inc.) and 66% zinc oxide powder.The polyacrylic acid was first dissolved in water, the carbon powderadded and the mixture mixed then blended in a high speed blender. Thewater was removed from the mixture by filtering and drying. The carbonfibers and polypropylene were added and the material melt blended.Finally, the zinc oxide was added and melt blended with the otherpreviously mixed constituents. The resulting mixture was formed into asheet of about 0.1 cm thickness and cut to form two pieces about 2 cm×2cm. The two pieces were then placed on either side of a copper platedstainless steel screen and hot pressed into a one piece component. Thezinc oxide was then reduced by standard electrochemical methods to formthe free zinc. The O⁻⁻, OH⁻ and H⁺ ions are readily transported throughthe electrode as are the electrons to complete the electrochemicalreactions.

The above described Daniell cells were rerun with the novel zincencapsulated electrode and repeatedly charged and discharged with noevidence of deterioration of the zinc electrodes other than minorsurface roughening over weeks of testing.

Similarly, other metals and materials can be encapsulated by, forexample, first compounding 27% acrylic acid of molecular weight of about4,000,000 (Carbopol) 940, a product of B. F. Goodrich Company); 7%carbon powder (Vulcan XC-72, manufactured by Cabot Corporation); 13%unsized 1/4 inch carbon fibers (Fortafil 3, supplied by Great LakesCarbon Corporation), 53% polyproplyene (Pro-fax PC072, manufactured byHimont U.S.A., Inc.) by melt blending as described above. The materialto be encapsulated is then added in a ratio of about 1 to 1.5 of theabove mix to the added material. An electrode with encapsulated silveroxide was found to operate with about the same current density ascommercial sintered silver oxide electrodes. An electrode encapsulatinglead powder was found to have equal or greater utilization when comparedto commercial electrodes.

The results of zinc/copper batteries are given in the following tablewhich lists the open circuit voltage, measured cell resistivity andcalculated maximum power output for the different pH combinations of theelectrolytes.

    ______________________________________                                        Electrodes     V oc     Ri        Power                                       Zn anode                                                                              Cu cathode Volts    Ohm-cm.sup.2                                                                          mWatts/cm.sup.2                           ______________________________________                                        acid    acid       1.1      40      8                                         acid    base       1.1      80      4                                         base    acid       1.3      20      21                                        base    base       1.3      65      7                                         ______________________________________                                    

The membranes employed in the acid-acid and base-acid cells were thesame as described above for Example 20 while the membranes for the othertwo were 16% Union Carbide Corporation 4,000,000 molecular weightpolyethylene oxide sold under the trade name "Polyox 301"; 8 percentactivated carbon powder sold under the trade name "Vulcan XC 72R" byCabot; 10 percent 1/4 inch unsized carbon fibers sold as Fortafil* 3supplied by Great Lakes Carbon Corporation; and 66 percent Dow ChemicalCorporation polyvinylidene chloride sold under the trade name "Saran 864resin".

The high conductance obtainable from the high content hydrogel membranesof this invention and the negligible diffusion make these membraneshighly desirable for battery separators. The lack of diffusion keepselectrolytes from mixing and hence contributes toward an extended shelflife of a battery.

Another advantage of the use of membranes of this invention is that anoptimum electrolyte can be used with each electrode, and hence,increased cell voltage can be obtained. It should also be noted thatsince the power output of a cell is proportional to the square ofvoltage (P=V² /R), a small increase in cell voltage can yield a verysignificant increase in power or energy per cell. For example, in azinc/manganese battery where the zinc half cell is alkaline and themanganese dioxide is acid, the employment of a membrane in accordancewith the examples of this invention will result in a battery voltagewhich approaches 2.05 volts (Zn/⁻ OH=1.25 volts and H⁺ /MnO₂ =0.80volts). The latter represents a 37% increase in voltage and an 85%increase in power over the conventional "drycell" battery. Experimentalcells employing the electrochemical selective membranes of the presentinvention have demonstrated current carrying capability equal to that ofstandard construction and were also rechargeable.

EXAMPLE 24

An example of an application of the present invention is a high voltagerechargeable battery. The battery used a membrane constructed of 37%acrylic acid of molecular weight of about 4,000,000 (Carbopol 940, aproduct of B. F. Goodrich Company); 10% carbon powder (Vulcan XC-72,manufactured by Cabot Corporation); 53% polypropylene (Pro-fax PC072,manufactured by Himont U.S.A., Inc.) by melt blending as describedabove. One half of the cell is a standard alkaline cell with a zincanode and the other half is a standard acid cell with a lead oxidecathode. A Zn/6N KOH//6N H₂ SO₄ /PbO₂ battery was constructed andtested. The test battery had an open circuit voltage of about 2.9 volts.This open circuit voltage compares with a lithium battery. The currentdensity of the battery was comparable to that of a standard alkalinezinc battery. The chief reactions can be simply diagrammed as follows:##STR4## The cell can be recharged by applying an external voltagesource which reverses the arrows and the signs of the electron and theproton terms.

EXAMPLE 25

The membranes of the present invention may be employed to make aconventional "drycell" battery completely rechargeable. Conventionaldrycell or alkaline batteries are not fully rechargeable because zincdiffuses into the manganese dioxide over time and is not recoverableduring the charging cycle, thereby poisoning the manganese dioxide. Acommercial Leclanche drycell battery was disassembled and the paperseparator was replaced with a membrane constructed of 30% Union CarbideCorporation 4,000,000 molecular weight polyethylene oxide sold under thetrade name "Polyox 301" and 70 percent Dow Chemical Corporationpolyvinylidene chloride sold under the trade name "Saran 864 resin". Thelatter modified cell was found to deliver a current equal to theconventional dry cell. In addition, the modified cell could berepeatedly deeply discharged and charged, limited only by irregularreplating of the zinc.

EXAMPLE 26

The use of the membranes of this invention allows the use of fuels suchas sugar, alcohol or carbon in batteries or fuel cells at roomtemperature. For instance, a cell consisting of a membrane prepared from25 percent Union Carbide Corporation 4,000,000 molecular weightpolyethylene oxide sold under the trade name "Polyox 301" and 75 percentDow Chemical Corporation polyvinylidene chloride sold under the tradename "Saran 864 resin", separating a 5N KOH anolyte and a catholyteconsisting of saturated sucrose solution with 10% nitric acid, wastested as a battery. When a platinum electrode was used in the catholyteand zinc used as the anode, an open circuit voltage of 2.4 volts wasobtained with a cell resistivity of about 3 Ohm-cm². When platinum wasused in both electrolytes, an open circuit voltage of 1.1 volts wasobtained with a cell resistivity of about 28 Ohm-cm². If the catholyteis replaced with a saturated solution of strontium nitrate with 10%nitric acid with a carbon cathode and the anolyte replaced with a 5N KOHsolution saturated with K₃ PO₄ and a platinum anode, an open circuitvoltage of 2.5 volts is obtained with a cell resistivity of about 3Ohm-cm².

EXAMPLE 27

Another application of a membrane in accordance with the presentinvention is in "flow" batteries which employ the change in valence oftwo metal ions in two electrolytes connected with a membrane. One of themetal ions is oxidized while the other ion is reduced during chargingand the reverse takes place during the discharge process. Anexperimental iron//copper battery employed a 30% iron sulfate and a 20%copper chloride electrolyte. The electrolyte was separated with amembrane of the present invention. The membrane was composed of 30%polethylene oxide in a polyvinylidene chloride matrix. The experimentalbattery had a carbon anode and a steel cathode. The experimental batteryproduced about 10 watt hours per gallon of electrolytes or approximately1.2 watt hours per pound.

It is known that an emf is developed between two electrodes placed intwo different electrolytes when separated by a membrane. This phenomenonis well recognized and is quantified by the Nernst equation of physicalchemistry which relates an emf to the log ratio of the activities of thetwo different electrolytes. The activity is nearly equal to theconcentration of an electrolyte so a membrane can be used to measureconcentration differences or the developed emf can aid in certainelectro-chemical processes. The theoretical emf according of the Nernstequation for single electron reactions at room temperature is 0.059volts per factor of ten difference in activities or concentration.Conventional pH sensors use a thin glass membrane which passes onlyprotons to measure the concentration difference of proton of hydrogenions on either side of the glass membrane. The voltage change of themost pH measuring cells is slightly above 0.05 volts per factor of tenchange in the measured electrolyte concentration. If the fragile glassmembrane is replaced with a membrane of this invention, the same voltageto concentration relationship is found, but with other advantages.

The glass membrane used in pH probes cannot pass significant currentthereby requiring expensive high input impedance voltmeters. To minimizepolarization effects, bulky and complex reference electrodes andelectrolytes are required.

EXAMPLE 28

A simple pH measurement cell was constructed of a membrane as describedin Example 2 above. The membrane separated a standard electrolyte of0.1N H₂ SO₄ and the solution to be tested. Two identical stainless steelwires of 0.023 cm were cleaned and used as the two electrodes. The slopeof the voltage/decade concentration change was equal to 0.052volts/decade which is comparable to present state of the art of pHmeasurement probes. Since the membrane is capable of passingconsiderable current, the stainless steel wires can be "cleaned" ordepolarized with a controlled electrical current prior to usage.

The pH, concentration or activity differences can be measured using themembranes of this invention with a reversible current source and a lowimpedance voltmeter. The difference in the cell voltage as a constantelectric current flows first in one direction through the cell and thenin the other through non-reactive electrodes, is proportional to theconcentration difference. The difference in voltage is equal to twicethe emf across the membrane.

EXAMPLE 29

Free chlorine in solution was measured in two electrolyte cells using amembrane according to Example 2 above and with measurements of the opencircuit voltage. In this case, a reference electrolyte was used. Thereference electrolyte consisted of a saturated solution of K₃ PO₄brought to a pH of 3.4 by adding phosphoric acid. An electrode of 50%tin and 50% lead was placed in the reference electrolyte. The unknownsolution consisted of varying the concentration of a sodium hypochloritesolution. The unknown solution had a copper electrode. This exampleyielded a slope of 0.068 volts/decade. The increase in slope may be dueto the use of an "active" cell wherein the cell functions as a batterywith protons flowing rather than in the normal "passive" type cellscurrently in use.

EXAMPLE 30

The materials of this invention can be used as membranes to change thepH of solutions as exemplified by the following demonstration whichcauses a change in color to occur in an electrolyte when an electricalcurrent is passed through a cell using the membranes of this invention.The membrane was constructed of: 37% hydroxyethyl cellulose, asCellosize* QP4400-H supplied by Union Carbide Corporation, 12.5% ligninsulfonate, Lignosol* FTA supplied by Reed Lignin, Inc. and 50.5%polypropylene resin supplied as Pro-fax PC072 by Himont U.S.A., Inc. Theingredients were melt/mixed at about 180 Celcius and formed into a sheetof about 0.02 cm thickness and then soaked in water for about 24 hours.The membrane separated two electrolytes which were both a 10% K₂ HPO₄and 0.02% phenolphthalein solution. When an electrical current waspassed through the two electrolytes using platinum electrodes, the pH ofthe catholyte (negative) would increase and the red color would appear,whereas the pH of the anolyte would decrease and its color woulddisappear. A pH difference of more than 2 pH points could readily beobtained and remained constant for weeks. The effect could readily bereversed by applying a reverse electrical current allowing eachelectrolyte to alternate between being a clear or red colored solution.Such a phenomenon is useful for display devices and different colors canbe obtained by using different pH indicators or pH sensitive dyes andthe like.

EXAMPLE 31

The flow of protons can change the pH of both electrolytes with theanolyte becoming more acid with a decreasing pH while the catholytebecomes more alkaline with an increasing pH. A cell using a membranedescribed in Example 2 and containing two identical smooth platinumelectrodes both immersed in distilled water with an initial pH of 4.6,was connected to a 10 volt source. The catholyte reached an equilibriumpH of 5.7 while the anolyte developed a pH of 2.5. The difference in pHremained constant for hours during the test with discontinuance of theelectrical current, but could be reversed with a reversed current flowyielding the same values in the new anolyte and catholyte. Theexplanation for this unexpected result may be due to reversibleelectrochemical reactions with absorbed CO₂, the formation of H₂ O₂ orabsorption of ions on the surface of the membrane.

The membranes of the present invention may be used with electrolyzersand other electrochemical cells so that added efficiencies may beobtained by operating each half cell in the optimum pH electrolyte. Byoperating the hydrogen generating electrode or cathode in an acid andthe oxygen electrode in an alkaline electrolyte, the voltage necessaryto electrolyze water can be significantly reduced to a theoretical emfof 0.41 volts (2H+2e⁻ =H₂ at 0.0 volts, and 4OH⁻ =O₂ +2H₂ O+4e⁻ at 0.41volts). Two unexpected phenomena were observed in attemptingelectrolysis at reduced voltage using the membranes of this invention:The first is the ability to maintain a constant current which would notbe possible without a chemical reaction between the acid and base andthe second is the reversibility of the chemical reaction. If (forinstance) a concentrical permselective cationic membrane were used, thealkali metal ion could diffuse through the channels of the membrane andreact with the acid in the catholyte forming a salt. Such a reactionwould not be reversible. The use of the membranes of this inventionallow the transport of both anions and cations resulting in a reversiblereaction. The electrolysis of water with less electrical energy than theGibbs free energy can only be obtained with the coupling of chemicalenergy to the electrochemical reactions. Some of the unexpected resultsof using the membranes of this invention are summarized in FIG. 2 whichrepresents the current/voltage curves of a typical electrolyzer cellusing the membrane of example 5 above or from a melt/blend of acrylicacid bound to carbon in an inert matrix such as: 37% acrylic acid ofmolecular weight of about 4,000,000 (Carbopol 940, a product of B. F.Goodrich Company); 10 percent activated carbon powder sold under thetrade name "Vulcan XC 72R" by Cabot Corporation; and 53 percentpolypropylene resin sold under the trade name "Pro Fax PC072". Smoothunblackened platinum electrodes are used to eliminate additional emfscaused by electrode/electrolyte interactions.

FIG. 2 shows a cell operating at less than the heat of formation (deltaH) which is about 1.5 volts and less than the Gibbs free energy (deltaG) of about 1.2 volts when the cell is 1) operated at low currentdensity levels, and 2) with an acidic catholyte and a basic anolyte.Curve 40 shows the unexpected linear current versus voltage curve as thecell is first energized with the reduced intercept voltage less than thetheoretical minimum voltage (free energy) for electrolyzing water. Ifthe voltage is reversed, as shown in curve 50, a much higher voltage isrequired (the theoretical emf is 2.057 volts: H₂ O+2OH⁻ =1/2H₂ +e⁻ at0.828 volts plus; 2H₂ O=O₂ +4H⁺ +4e⁻ at 1.229 volts), but the resistanceof the cell is slightly lowered with the current linear with respect tothe applied voltage. If the temperature is increased to 50 degreesCelsius, with the current flow in the initial direction, the resistanceof the cell drops indicating an activation energy greater than 9kJoules/mol as shown in curve 60. The electrolysis at less than 1.2volts indicates an electrochemical reaction other than the expected andanalysis of the electrolytes indicates that the following complexreversible electrochemical reaction occurs: ##STR5## where the sulfateand sodium ions traverse the membrane while the electrons aretransferred with the applied current. If the current is reversed, thesodium and sulfate ions return to their original electrolytes and the pHof each electrolyte approaches the original value as may be diagrammed.##STR6##

The simultaneous transfer of both anions and cations through themembrane results in the transfer of chemical energy between the twoelectrolytes which is equated to the energy of the electron transfer.The membrane serves, therefore, as a coupler in the conversion ofelectrical energy into chemical energy or vice versa. The production ofan acid, and base with the hydrogen and oxygen is not expected and maybe explained because of the novel coupling of the chemical energy of theacid/base reaction to the electrochemical reaction and vice versa.

It is to be noted that such a reverse reaction could not take place witha commercial permselective membrane since only ions of one charge coulddiffuse through the membrane. For the reverse reaction above, moreelectrical power is supplied than for the forward reaction.

An electrolyzer cell using a membrane constructed of melt/blended 30%polyethylene oxide of molecular weight 600,000 sold under the trade nameof "Polyox 205" by Union Carbide Corporation and 70% polyvinylidenechloride resin sold as "Saran 864" by Dow Chemical Corporation, andplatinum electrodes, and filled with 1N H₂ SO₄ in the catholyte and 1NKOH in the anolyte; showed the reversal in the pH with current flowindicating the exchange of the acid and base with the rate as expectedby Farraday's law and the above explanation.

The "normal" exponentially increasing current versus voltage curve isshown in curve 70 when both of the above electrodes are in a 1N NaOHelectrolyte without a membrane. As the cell with the membrane operates,the pH of both electrolytes shift toward each other and then reverses,but if the current is reversed, the pH of each electrolyte can bereturned to its original value.

The effect of varying the hydrogel content and the effect of temperatureupon the voltage-current relationship is shown in Table 4 where "Vforward" is at least squares fit to the data obtained from the currentvoltage measurements. The initial voltage is therefore the first termand the resistance is the slope or multiplier of the current I. Thecatholyte in all cases is 1M H₂ SO₄. The membrane area is 8 cm². Thearea of each platinum electrode is 3.3 cm² with each electrode about 1cm from either side of the membrane. The voltage is measured as thecurrent is varied from 0.005 to 0.100 Amperes.

                  TABLE 4                                                         ______________________________________                                        Sample Anolyte    Temp .sup.- C.                                                                          % HYD   V Initial                                 ______________________________________                                        1      1M KOH     25        20      0.96 + 150*I                              2      1M KOH     25        25      0.98 + 18*I                               3      1M KOH     25        30      1.00 + 10*I                               4      1M NH.sub.4 OH                                                                           25        30      1.36 + 17*I                               5      1M NH.sub.4 OH                                                                           31        30      1.32 + 15*I                               6      1M NH.sub.4 OH                                                                           47        30      1.20 + 12*I                               ______________________________________                                    

The rate of transport of different ions through the materials of thisinvention appears to be closely proportional to their conductance atinfinite dilution in water. An experimental cell was constructed using amembrane constructed of 22 percent Union Carbide Corporation 4,000,000molecular weight polyethylene oxide sold under the trade name "Polyox301"; 11 percent activated carbon powder sold under the trade name"Vulcan XC 72R" by Cabot; and 67 percent polypropylene resin sold underthe trade name "Pro-Fax PC072" by methods outlined above. The anolytewas a 4% NaOH and 5.6% KOH solution while the catholyte was a 10% H₂ SO₄solution. Platinum was used as the electrodes. Three samples werecollected after three different elapsed ampere hours and analyzed.Potassium was found to be transported at a ratio of 1.6:1 to sodiumwhich approaches the ratio of 1.5:1 for their ratio of conductances atinfinite dilution in water. Similarly, copper is found to approach the6.4:1 ratio of hydrogen to copper conductance at infinite dilution inwater.

Fuel cells can also have an increased electrical output by coupling thechemical energy of two electrolytes. For instance, if the anolyte ismade alkaline and the catholyte made acidic for the normalhydrogen-oxygen fuel cell, then the theoretical voltage is increasedfrom 1.2 to 2.0 volts with the following half cell reactions:

    ______________________________________                                        anode:    H.sub.2 + 2 OH.sup.-  → 2H.sub.2 O + 2e.sup.-                                              0.828 volts                                     cathode:  O.sub.2 + 4 H.sup.+ 1.229arw. 2H.sub.2 O - 2e.sup.-                 total cell emf:               2.057 volts                                     ______________________________________                                    

The electrochemical reactions can be diagrammed as ##STR7##

As explained for the electrolyzer above, the increase in cell voltage isdue to the added chemical energy of the acid and base. After the acidand base have reacted, they may be regenerated by applying an electricalcurrent. A cell made with the membrane of example 5 above and with 20%NaOH in the anolyte and 10% H₂ SO₄ in the catholyte and with unblackenedsmooth platinum electrodes, yielded 2 volts open circuit when theelectrodes were covered with hydrogen and oxygen.

EXAMPLE 32

One important aspect of the present invention is the ability of theionic semiconductor materials to split water into its composite ions.This ability is exemplified by the following experiment. Two identicalstrips of platinum, each with an active area of 0.3 cm2 area, wereselected as electrodes with one of the platinum strips being coveredwith an ionic semiconductor prepared from 30% Polyox 301 (UnionCarbide), 20% phenol-formaldehyde 12704 (Durez) and the remainder beingpolypropylene (Hooker Chemical). The constituents of the ionicsemiconductor were melt-mixed and pressed to about 0.5 mm thickness. Thetwo electrodes were placed together in a 50 ppm sodium hypochloritesolution at room temperature and the open circuit voltage as well as thevoltage when connected to a 100,000 ohm load were recorded.

A voltage of over 50 millivolts could be maintained at room temperaturewith the resistive load connected, indicating that a continuous currentwas being produced. The open circuit voltage was about 0.2 volts.Heating the cell to about 50 degrees C raised the open circuit voltageto 0.5 volts and the voltage across the 100,000 resistor to 0.25 voltsdemonstrating a significant increase in power output with increasedtemperature.

The following novel "water splitting" reaction at the ionicsemiconductor covered anode is assumed to explain the continuous currentproduction and high activation energy or temperature dependence. (Thedouble slash, //, is used to indicate the nonporous junction with theionic semiconductor and the ion and electron transfer between the twohalf cells is indicated by lines drawn between the two electrodeequations.) ##STR8##

If the experiment is repeated without the ionic semiconductor coating onthe one platinum strip, no voltage or current is observed.

The novel results can be explained by assuming that a water molecule inthe presence of the bound hydrogels - and with sufficient thermal energyis able to `split` into its constituent ions. Increasing the temperatureincreases the numbers of water molecules with sufficient thermal energyto split. Such a high concentration of splitting is normally notencountered except under high electrostatic fields or in the presence ofhigh pressure and temperature with a catalyst. Further examples of watersplitting are given in some of the following examples

EXAMPLE 33

Films formulated from a flexible matrix material and a hydrogelaccording to the teaching of this invention are useful for providing aprotective and `breathable` interface between the dermis or epidermis ofa body and the ambient environment. The membranes of this invention arebelieved to function in a manner similar to natural biological membranesand are `breathable` or can pass perspiration or body exudates at or inexcess of the normal rate of production of the body; are bioadhesive orcan bond to the epidermis or dermis; provide `active` oxygen or protonsthrough water splitting; and can be bonded to a supporting fabric. Allof these characteristics are achieved while providing a protectivebarrier to rain, chemical hazards, infectious material or agents, dirtetc.

The film may be applied to the skin or subdermal flesh by means of thedirect application of a fluid which contains the solid constituentswhich form the film on drying or by the direct application of apreformed film either pre-moistened or moistened by the exudate of thesubdermal flesh. The film can be kept in place for days without theexpected formation of an exudate interface or scab since the film,because of its tight adherence to the dermis, functions as would thenatural skin. It is believed that the film also furnishes ions throughwater splitting (as discussed in Example 32) which aids in fasterhealing of the wound. If the films are flexible and thin there is nosense of discomfort and very little awareness of its presence.

The film may also be applied adjacent to the skin by either a standardwound type dressing, wherein the film is either self supporting, orthrough use of a composite of the film with a supporting structure thatholds the film adjacent to the body.

The film may also be as a stand alone film or incorporated on or in afabric which provides protection for the body or parts of the body suchas in outer garments for rain protection or completely closed garmentssuch as worn for environmental protection against hazardous chemicalsand the like.

The advantages of this novel protective film are therefore: the abilityof the film to be: 1) self adhesive either to the epidermis or dermis orto a supporting fabric or matrix with suitable initiation by water, heator pressure, 2) compatible with the processes of the body, 3) able totransport water equal to the normal exudate rate of the body, 4)sufficiently strong to provide mechanical protection, 5) impenetrable byunionized matter, 6) able to provide hydroxyl or hydrogen ions fortissue rebuilding, and 7) of low inherent cost.

A liquid ionic semiconductor formulation incorporating a flexible matrixand a hydrogel is as follows: 4 grams hydroxyethylcellulose or HEC as`Cellosize` QP 100000-H as supplied by Union Carbide.

94 grams polyurethane dispersion as `NeoRez R- 963` supplied byPolyvinyl Chemicals which contains 34% by weight of polyurethane. TheHEC is ideally first dissolved in water and then added to the liquidurethane mixture during mixing. Water must generally be added since theHEC is a thickener and otherwise the mix would be too thick. (It shouldbe noted that hydrogels have been added to coating solutions in the pastto control the viscosity, but in these cases the amount of addedhydrogel was been at a considerably lower lever (typically less than 1%)than is used in ionic semiconductive materials.)

Hydroxyethylcellulose, HEC, can be added and mixed with the polyurethaneto form a non-leaching membrane. One advantage in using HEC inpolyurethane is that a `non-blocking` or non-sticky film can beobtained. Most urethane sheets have blocking and will adhere tothemselves to some degree which results in a `tacky` feeling of theurethanes. Films formed from HEC and polyurethane provide a silky softfilm which is a strong advantage for clothing or garment applications.

Polyurethane has been discovered to provide sufficient bonding to manyof the hydrogels so that additional coupling agents and the like are notrequired. An example of urethane functioning as a coupling agent isprovided in the following example of a solid plastic capable of beingextruded or formed with conventional plastic equipment:

An amount of 1 gram of polyethylene oxide supplied as Polyox C014 byUnion Carbide, 0.5 gram of urethane (ester based) solid resin suppliedas Q- Thane PS455-100 by K. J. Quinn and Co., and 2 grams ofpolyvinylidene chloride supplied as Saran Resin 864 by Dow Chemical weredry mixed together, melt mixed at about 350 degrees F and then extrudedin a sheet of about 0.02 inches thickness. The sheet was found to absorbabout its own weight in water with a conductance of less than 20ohms-cm2 in a Cu/CuS04//H2S04/Pt test cell as described earlier. Thenovel membrane has no detectible copper passage after one hour ofoperation.

A very good liquid film can be produced using pectin. The followingformulation is by dry weight of the active ingredients and not of theemulsion or solution weight. The final dried film consisted of about 25%by weight of pectin. The formula consists of: 20.8 parts vinylacetate/ethylene supplied in an emulsion from Reichhold as Elvace 1870,5.2 parts of pectin supplied in a solution by General Foods Corp. underthe name Certo. The ingredients were mixed together in a high speedmixer to a uniform consistency and then coated on a substrate or cast asa free standing film.

The physical characteristics of a film in accordance with this inventionare essentially those of the supporting plastic matrix unless the filmis saturated with water, in which case there is expansion, softening andwhitening similar to natural human skin.

Thin films as described above can be constructed having water vaportransmission rates greater than 3000 grams/day-m2 when measured by ASTME 96-80 Procedure B. It should be noted that the vapor pressuredifferential in the above test which drives the water vapor throughnormal porous materials is not required for the films of this invention.The water transmission rates of the films of this invention are limitedin general by the rate of water removal or evaporation rather than bywater `take-up`. For instance, if a polyurethane film as described aboveis brought into contact with water, it can exhibit a water absorptionrate much greater than 5000 grams/day-m2 at 100 degrees F. Since theenergy for ion transfer is thermal, there is a strong temperaturecoefficient for the absorption rate.

The films of the invention can be produced with a wide variety ofsupporting plastics as well as with varying amounts of added activepolymers to vary the water vapor transfer rate or the resistance towater swelling.

Pigments can be added to the ionic semiconductor materials to matchnormal skin coloration such that the materials can be used for cosmeticrebuilding, covering of skin defects or normal cosmetic purposes.

EXAMPLE 34

Selective proton or hydroxyl transfer through the novel membranes of theinvention can be obtained by providing an inert hydrogel depletionjunction between the membranes and the external liquid which serves as abarrier for all but protons and hydroxyls. Such a junction consists of athin layer of a matrix material functioning as a thin hydrogel deficientregion perhaps corresponding to an `intrinsic` conduction region inelectronic semiconductors.

For example, Kraft paper can be coated with a solution consisting of a40% polyethylene (Union Carbide 301) and a 60% Phenolic (Durez 12704)prepared as described in Example 9. After the mixture has dried but notfully cured, it is coated with an additional thin layer of phenolic,dried and then the combined films cured.

The double coated paper was then tested in the precedingCu/CuS04//H2S04/Pt test cell for both conductance and copper transferthrough the novel membrane.

The (dc) conductance of the combination was not quite as good as wouldbe obtained with just the novel membrane coating, which is about 10Ohm-cm2, but was nonetheless quite good at about 80 Ohm-cm2. The coppertransfer was immeasurable after 2 hours, compared with about a 6% ratefor the single uncoated film.

A phenolic film without the hydrogel/phenolic coat would not be expectedto pass a significant electrical current.

The conclusion is ,therefore, that the novel membranes split water, asassumed, and the protons are able to be pass through the phenolic. Ifthe current is reversed then hydroxyl ions are passed through the novelmembranes.

For membranes formed as described in preceding examples, increasedselectivity for protons may be explained by the formation of an outer`skin` of the matrix material with a lower hydrogel content than thebody of the membrane during fabrication.

EXAMPLE 35

The membranes of this invention may be used to provide a novel method ofpurifying water . Since the ions of water have many times the transferrate of other ions, membranes constructed according to the teachings ofthis invention can be used to reduce the impurity content of water.Since the membranes are depletion driven, purified water can be absorbedfrom one side while contaminated or salt water can be made available atthe other surface. One application would be in supplying water for cropsby pumping sea water or polluted water through tubes or troughs made orcoated with the films of this invention which are placed under ground oradjacent to the root systems of the plants or crops to be irrigated. Thenovel membranes have the capability of providing purified water only asneeded to the roots or soil leaving the bulk of the salt behind in themain stream of water.

The membranes of this inventions will transport water only as long aswater is being removed from one surface and supplied at the other. Therate of transfer of the water is a function of the temperature (beingincreased with increased temperature), the rate of removal of the waterfrom the purified side, and the percentage of hydrogel in the membrane.

Films with a thickness greater than 0.005 cm or so can be easilyevaluated for a conservative comparative water transmission (assuming aninfinite drain) by measuring the rate of water take-up as well as bytotal water absorbed. The standard water vapor penetration tests likeASTM E 96-80 are not directly applicable since the pressure differencebetween the heated interior of the container and the ambient cannotdrive water vapor though the non-porous ionic semiconductors. Thepreferred measurements consist of measuring the area of and weighing (1)the sample as prepared, inserting the sample in water heated to about 40degrees Celcius for one minute, blotting dry, weighing (2) and insertingagain in water for two minutes, blotting dry and weighing (3), and thenleaving the sample in the water for several hours or until absorption iscomplete and then blotting dry and weighing (4). The difference inweight between weighings (2) and (3) is divided by the area of thesample, multiplied by 720 (weight gain/cm2 in 24 hours) times 104 toobtain grams per 24 hours per square meter. This number is divided bytwo to obtain the water transmission rate for one side. The total watertake-up is expressed as the ratio between weights (1) and (4) or(1)/(4).

Table 5 below lists some results:

                  TABLE 5                                                         ______________________________________                                        %                            Rate     Ratio                                   wt.     Hydrogel  Matrix     g/m2-day dry/wet                                 ______________________________________                                        25      HEC       Urethane A 15,000   0.41                                    20      HEC       Urethane A  9,000   0.53                                    20      HEC       Urethane B 33,000   0.29                                    20      Starch    Vinyl acetate                                                                            12,000   0.60                                    20      Pectin    Vinyl acetate                                                                            20,000   0.57                                    ______________________________________                                         where:                                                                        HEC is hydroxyethyl cellulose as `Cellosize` QP 100000H supplied by Union     Carbide.                                                                      Starch is `ARGO` corn starch supplied by Best Foods                           Pectin is supplied in a solution under the trade name `Certo` by General      Foods Corp.                                                                   Urethane A is a polyurethane dispersion `NeoRez R963` supplied by             Polyvinyl Chemicals                                                           Urethane B is a polyurethane dispersion `NeoRez R966` supplied by             Polyvinyl Chemicals                                                           Vinyl Acetate is a vinyl acetate/ethylene emulsion supplied by Reichhold      as `Elvace 1870`.                                                        

It should be noted that the above tests do not indicate the maximum rateof water take-up since that would occur during the first moments ofinsertion in the water. In applications of the above formulations, thelimitations have not been found to be the rate of water take-up, butrather the rate of water removal from the drier side of the film.

The first item in the table, 25% HEC/Urethane A, with the rate of 15,000g/m2-day compares with the rate of 3,000 g/m2-day when measured by theASTM E 96-80 Procedure B. The difference is believed to be due to thelimited rate of evaporation from the exposed surface of the ASTM test.The 25% HEC/Urethane A film is also an excellent electropermeablemembrane with a dc resistance of less than 6 ohm-cm2 with a dc currentdensity of about 7 mA/cm2 when separating an acid 20% copper saltanalyte and a 10% sulfuric acid catholyte. The copper ion transport isless than 2% of the total ion transport. For a comparison, 20%Pectin/vinyl acetate film has a dc resistance of 5 ohms-cm2 and a copperion permeation equal to 4% of the total charge.

Other ions such as sodium and chlorine from salt may also be transportedthrough the membranes of this invention at lower transfer rates. Forsome crops and locations, the amount of salt passing through (less than10% of main stream content) may in practice be low enough to be of noconcern or even desireable for the mineral supply of the crops.

If a higher purity of water is desired, a thin coating of a matrixmaterial can be applied as described in Example 34.

An example uses two plastic tubes sealed at one end with theformulations described in Example 34 above. The tubes were placedupright upon absorbent toweling with the membranes of this invention incontact with the toweling. The tubes were filled with water and the openupper ends of the tubes were sealed. The tubes were weighed at differenttimes to determine water loss into the toweling which was assumed tofunction as absorbent soil.

The tube with the phenolic added coating had a transfer rate of nearlypure water of about 350 grams per day per square meter at roomtemperature. The second tube without the added phenolic coatingtransferred water at the rate of about 1500 grams per day per squaremeter.

If one assumes that novel membranes for this application have a life of10 years and can be film extruded to form practical water troughs ortubes at a cost of less than 50.20 per square meter, then the cost ofdelivered purified water from the first the novel membranes is about$160 per million liters ($0.60 per thousand gallons) and the cost ofless pure water from the second the novel membranes is about $36 permillion liters ($0.14 per thousand gallons) which is significantly lessexpensive than existing methods.

EXAMPLE 36

This example relates to an improved hydrogen electrode and applicationsthereof. Hydrogen electrodes have been used to provide a source ofhydrogen ions in electrochemical reactions, or measurements and haveconsisted of a simple electrode assembly wherein hydrogen gas is bubbledup on the surface of platinum or constructed of a complex porouselectrode assembly perhaps typified by an electrode assembly and itsapplications as described by Juda et al in U.S. Pat. No. 4,614,575.

The hydrogen electrode can take several forms. Thus, the electrode canconsist of a conductor coated with an ionic semiconductor wherein thesemiconductor behaves as both a solid electrolyte and the watersplitting element. Alternatively, the electrode can comprise an assemblywherein an electrolyte is disposed between the the semiconductor and theconductor.

The novel hydrogen electrode of this invention differs markedly from theexisting hydrogen or gas diffusive electrodes in that the existingelectrodes require the continual introduction of hydrogen gas intoideally a porous catalytic anode whereas the electrodes of thisinvention rely upon water splitting at the surface of an ionicsemiconductor to supply hydrogen ions and no hydrogen gas is required. Afurther advantage is that the anode does not have to be a catalyst andpoisoning of the electrodes is not a problem.

An experimental cell was constructed with two chambers which wereseparated by an ionic semiconductor which was obtained from a coatednylon fabric with a film prepared from the following formulation: 60 gpoly(ethylene oxide), supplied as Polyox 301 from Union Carbide; 40 gphenolic resin, supplied as 12704 from Durez; 200 g PVDC latex, suppliedas RAP 184 from Dow Chemical Corporation. The poly(ethylene oxide) andphenolic are first dispersed in 2-ethoxyethanol and then mixed togetherwith water under a high shear to form an associated product and then thelatex is added and mixed together. The coated fabric was dried and thenheated to cure the film.

A 5% KOH solution anolyte and a platinum anode were placed in onechamber. The catholyte contained a 5% sulfuric acid solution to whichwas added copper sulfate to obtain an initial solution strength of about800 ppm of copper. An aluminum electrode was inserted as the cathode. Aconstant current was applied to the cell of about 1mA per squarecentimeter of the ionic semiconductor producing a minimum cellresistance of about 200 ohms-square centimeter of the ionicsemiconductor. The voltage dropped initially quite rapidly and thenslowly increased as the copper was plated out of the catholyte onto thecathode. The voltage of the cell started at about 1.4 volts, droppingand then finally reaching about 2 volts when the experiment was stopped.After 45 minutes, the aluminum was weighed and the weight gain indicatedthe removal of the inserted copper.

Without the separating membrane, little copper can be plated out even atlow current efficiency

The above cell and this invention can described by the following diagramand electrochemical equations which relate to the removal of dissolvedmetals in water. ##STR9## where M+ is a metal ion and C- is theassociated complex. The above electrochemical reactions were written fora metal ion of valence one, but it should be understood that thereaction would also apply for other positive ions or other valences

The catholyte side of the membrane can be seen to be functioning as if aconventional hydrogen electrode were being used injecting hydrogen ionsinto the electrolyte. Since the membrane is non-porous, other ionexchanges at the anode are negligible as for instance, the C-complexesare prohibited from passing through the membrane.

The use of the KOH solution in the above experimental cell illustratesanother advantage of using the novel hydrogen electrode assembly sincethe operating voltage can be reduced resulting in lowered electricalpower requirements by utilizing the entropy increase of KOH as describedin Example 31. It should also be obvious that other combinations ofelectrolytes can also be used.

EXAMPLE 37

It has been discovered that the novel membranes containing anelectrically conductive element or a current collector may be used toreplace porous oxygen or gas electrodes for electrochemical cells. Suchelectrodes, when interfacing with air or oxygen, reduce the oxygen andtransfer the ions to the electrolyte.

The prior porous gas electrodes use porous conductive materials madeform or coated with catalytic materials such as platinum which enhancethe reduction of oxygen. The first such electrode made over a hundredyears ago, consisting of mixed carbon and platinum powder, is stillexemplary of the existing gas electrodes.

The conductive membranes of this invention differ considerably from theprior art in that they are non-porous with the initial ionization of thegas, ion transport, electron transfer, and ionic injection assumed totake place in four different areas and medias, (1) the gas/membraneinterface, (2) The interior of the membrane, (3) the membrane/conductorinterface, and (4) the novel membrane/electrolyte interface.

A conductive membrane may be constructed by coating a porous electricalconductor with an ionic semiconductor material such that the compositeis rendered non-porous or the voids are filled with the added material.It is preferable that the conductor is covered on both sides. Forexample, a perforated platinum sheet or a stainless steel screen can besandwiched between two sheets of a thermoplastic membrane with heat andpressure, or the conductors can be coated with a water or solvent baseddispersion or solution to form a covering.

A formulation which can be used to form thin membranes (films) for theapplication being described is as follows:

An amount of 3 grams of polyvinylidene fluoride as supplied by UgineKuhlman of America Inc. as Foraflon 1000 LD was, dissolved in 10 ml ofN-methyl 2 pyrollidone. An amount of 1 gram of polyethylene oxide assupplied by Union Carbide Corp. as WSR Coagulant Polyox and 0.5 gram ofpolyacrylic acid as supplied by BF Goodrich as Carbopol 940 weredissolved in 30 ml of N-methyl 2 pyrollidone and mixed under high shearto form an associated product. The two dissolved materials were finallymixed together and sufficient solvent added to form the properviscosity.

Variations of the matrix may be other dissolved polymers such aspolysulfone as supplied by Union Carbide as P-1700, a polyvinyl chlorideresin supplied by Borden Chemical as VC 440, polyvinylidene chloridesupplied by Dow Chemical as Saran 864. Other hydrogels can also be usedwith appropriate coupling agents such as polyurethane.

One of the above films is coated on a conductive porous material such asa non-woven carbon cloth obtained as 0.5 ounce/square yard 100% carbonfiber (1" long) from International Paper Company to form a conductiveelectrode.

A simple zinc/air battery offers an example of the application of thenovel non-porous conductive membrane. The battery is constructed usingone of the above novel conductive membranes as the oxygen ordepolarizing electrode. This conductive electrode separates a 10% KOHanalyte containing a smooth metal zinc electrode and the ambient air.The effective area of the zinc and novel conductive membrane are ofabout 6 cm2 area each. The electrodes are separated by about 1 cm.

At 24 degrees Celsius, the open circuit voltage of the cell is 1.2 Voltswith an internal resistivity of 2400 ohms-cm2 (equal to load resistanceto drop cell voltage to 1/2 of open circuit voltage). The maximumrelatively continuous power output is about 0.1 mW per cm2 of the novelconductive membrane

When the cell is heated to about 60 degrees Celcius, the open circuitvoltage remains at 1.2 volts, but the cell resistivity decreases toabout 1000 ohms-cm2 with a maximum continuous power output of about 0.4mW per cm2.

The resistance of the heated cell above can be further reduced by over30% by passing pure oxygen over the outer surface of the oxygenelectrode indicating the consumption of oxygen within the cell.

If instead of adding oxygen to the outside of the air electrode, it isbubbled into a solution of 10% sulfuric acid which in turn is in contactwith the novel conductive membrane by means of another addedcompartment, the open circuit voltage at room temperature remains nearlythe same at 1.2 volts, but the cell resistivity drops to about 700ohm-cm2 with a continuous power output of about 0.5 mW/cm2.

If the above cell with oxygenated sulfuric acid is heated, the cellresistivity drops proportional to temperature being about: 600 ohm-cm2at 29° C., 480 ohm-cm2 at 36° C., 430 ohm-cm2 at 44° C. and 400 ohm-cm2at 53° C.

Another unexpected result occurs when a small carbon rod with a 2 cm2area is inserted into the heated oxygenated sulfuric acid example aboveand electrically connected to the conductive membrane. The cell voltageincreases to 1.4 volts and the resistivity lowers further to about 300ohm-cm2 and delivers a relatively constant power of about 1.7 mW/cm2 atabout 60 degrees Celsius.

The results from this example are not expected since the connection ofan external electrode to the air electrode would not be expected tochange the cell operation and certainly not to improve the operation ofthe cell.

A further modification of the air cell results when the zinc anode ofthe above heated cell is replaced with a carbon electrode in a sugarsaturated 10% KOH solution. The cell is therefore: C/KOH-sucrose//C//H2SO4-02/C. Where the //C// represents the novel conductive membrane, andthe novel conductive membrane is connected to the carbon electrode inthe sulfuric acid. Such a cell when heated to 60 degrees Celsius, andwith oxygen bubbled through the sulfuric acid, has an open circuitvoltage of 0.7 Volts and can deliver a continuous current of 1 mA/cm2 ofthe novel conductive membrane area with a cell voltage of about 0.35Volts (representing a resistivity of about 350 ohm-cm2 for theconductive membrane area). Such a cell is in fact a fuel cell operatingon readily available and inexpensive materials and illustrates theunique characteristics of the novel conductive membranes.

A comparison of the above novel conductive membrane can be made withother membranes by exchanging the electrodes and electrolytes for aZn/10%-KOH//C//10%-H2S04/Pb02. In this example, a commercial lead oxideelectrode with an effective area of about 2.5 cm2 is used as well as theabove smooth zinc sheet. A polarization curve was run with the membranepotential drop measured with two reference cells placed adjacent to themembrane on either side. The current levels were maintained for twominutes before changing.

    ______________________________________                                        Amperes                                                                              0      0.025   0.100 0.200 0.300 0.500 V                               cell   3.00   2.89    2.73  2.55  2.31  1.73                                  delta-V                                                                              0      0.04    0.11  0.19  0.28  0.47                                  ______________________________________                                    

The membrane resistance is therefore less than 1 ohm or less than 6ohms-cm2. It should be noted that the cell is capable of delivering over50 mA/cm2 at a voltage of 2.31 volts or more than 100 mW/cm2 at avoltage well above the standard lead acid battery's open circuitvoltage.

EXAMPLE 38

The novel ionic semiconductive membranes are useful for constructingmembrane electrodes since: (1) There is no direct intraelectrolytecontact or exchange. (2) They are capable of maintaining significantcurrent flow with the voltage referenced to the analyte. (3) They havethe ability to furnish protons or hydroxyl ions at the junctioninterface by splitting water molecules with thermal energy. (4) They arehighly selective and only respond to redox ions which areelectrochemically involved in both electrode reactions. (5) Highlyselective electrodes can be obtained by adding an coating of the inertmatrix to the junction membrane.

Ionic semiconductive membrane electrodes can be made in two forms. Thefirst, type 1, is similar to the standard reference electrode consistingof an inner half cell but with the junction replaced by an ionicsemiconductor separator which can be of any of the formulations listedabove. The second, type 2, consists of a metal electrode enveloped with,coated with or contained within an ionic semiconductor material. Theionic semiconductor material in a type 2 electrode functions as a solidelectrolyte as well as providing the novel characteristics of the ionicsemiconductor. The ionic semiconductor material that is chosen can bebased on the bonding capability to the physical support of a probe, theconductance desired, the selectivity, the environment or temperature orease of fabrication.

Neither electrode is theoretically limited as to size. Since the ionicsemiconductor junction is non-porous, no electrolyte reserve for acontrolled leakage or buffer is required. Since the ionic semiconductorseparator is of relatively high ionic conductance, no area limitationsare normally imposed

The type 1 probe can operate with two different modes. The first mode isthe classical, wherein the electrode is oxidized or reduced with anelectrochemical reaction yielding or combining with ions which aretransferred through the membrane. The second mode of operation involveswater splitting at the membrane with a corresponding reduction ofprotonsor the oxidation of hydroxyl ions depending upon the polarity ofthe electrode. For a negative reference probe, the second mode can bediagrammed as: ##STR10##

The type 2 electrode which can operate also in either mode but may belimited in current density to only a few microamperes per squarecentimeter if the electrode is not a depolarizer or because of the timefor electrochemically generated gasses to diffuse away from themetal-ionic semiconductor junction. The type 2 electrode operates withthe ionic semiconductor material serving as a solid (polymeric)electrolyte as well as the ionic semiconductor as above. Miniature type2 electrodes can be constructed by casting a thin film from a solventbased ionic semiconductor resin onto a thin metal wire or carbon fiber.

A semiconductive membrane electrode of type 1 has been found to be anexcellent replacement for commercial reference probes when the innerhalf cell consists of a Class 1 electrode and the corresponding saltelectrolyte. An electrode was constructed by thermal bonding a membranemade as described in Example 13 above to a polypropylene tube with aninner diameter of about 0.4 cm and 6 cm length. The tube was filled witha 3 M KCl solution saturated with AgCl. The electrode was a silver stripabout 0.3×6 cm which had been electrochemically oxidized in a 10% HClsolution to form an AgCl coating on the silver.

The electrode was compared with commercial reference probes and found tooperate with equal or improved emf stability over a wide pH range and 3orders of magnitude of different salt concentrations including potassiumand sodium. The advantage being the lack of diffusion through the ionicsemiconductor as compared with the diffusion through the porousseparators of the commercial probes.

Type 2 membrane electrodes are found to be useful as referenceelectrodes in pH indication. As for example: a type two electrode can beconstructed by coating a small piece of clean copper with a solution of35% poly(ethylene oxide), supplied as Polyox C014 from Union Carbide andphenolic resin, supplied as 12704 from Durez as described in Example 9above. After the solution has been dried and partially cured, it iscoated with a second coat of the matrix Phenolic 12704, dried and bothcoats then cured. The coated copper type.2 membrane electrode can thenbe connected to a voltmeter with a Redox electrode such as platinumVoltage readings for the type 2 electrode coupled with platinum indifferent pH solutions are:

    ______________________________________                                        pH        1       4          7     10                                         Voltage   0.830   0.530      0.460 0.359                                      ______________________________________                                    

The type 2 electrode has a slow response since the electrolyte isdependent upon equilibrium of the conduction hydrogel ions and the outerelectrolyte and is not `buffered` as with the electrolyte of the type 1membrane electrode. The type 2 electrode has the advantage of small sizeand no maintenance.

EXAMPLE 39

A sensitive and stable measurement of free chlorine can made by using anoble metal and a type 1 or type 2 reference electrode as describedabove.

For example, a chlorine detector can be constructed using two copperwires with an active length of about 2 cm and a diameter of 0.3 cm. Oneof the wires is gold plated and the other is coated from a formulationsuch as 4 grams hydroxyethylcellulose or HEC as `Cellosize` QP 100000-Has supplied by Union Carbide dispersed within 94 grams polyurethanedispersion or as `NeoRez R-962` supplied by Polyvinyl Chemicals andwater.

When the two copper wires are inserted within a water solutioncontaining free chlorine, and connected to a voltmeter with an inputimpedance as low as 100k ohms, a sensitivity of over 150 mV/ppm at the 1ppm level is obtained. The sensitivity being proportional to the log ofthe concentration of the chlorine or decreasing with increased chlorineconcentration. Such a device has been found to operate continuously inswimming pools, hot tubs, spas and the like.

The following reaction is assumed to take place utilizing watersplitting: ##STR11##

EXAMPLE 40

The above type 1 or type 2 probes can be used in voltage/current typemeasurements since the conductance of the junction is sufficiently highsuch that voltage drops across the membrane are generally negligible iflow current densities are used.

For instance pH can be determined by using a type 1 membrane electrodefilled with a buffered electrolyte of pH 1.00 and with a platinumelectrode. The opposing electrode consists of another platinumelectrode.

The two electrodes are inserted into the unknown analyte and connectedto a reversible constant current source. The cell voltage is monitoredas the current flows first with one polarity and then the other forfixed periods of time.

With a time interval of 1 minute, typical measured emfs for different pHsamples are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                        Analyte pH                                                                             forward emf reverse emf                                                                              emf difference                                ______________________________________                                        10       2.341       1.677      0.664                                         7        2.420       2.185      0.235                                         4        2.064       2.182      0.118                                         1        1.614       1.571      0.043                                         ______________________________________                                    

The above yields the relationship: pH=11.5+3.35* log(emf difference).Similar results can be obtained by using a type 2 platinum strip exceptthat the type 2 may appear to have an inner basic rather than an acidicelectrolyte.

EXAMPLE 41

The material of this invention can be used in electrochemical capacitorsuseful as filter capacitors or in supplying electrical power duringshort power outages. A capacitor was constructed using two platinumelectrodes each with an area of 4 cm2. These electrodes were initiallyseparated by an anolyte and catholyte, each consisting of 30% Na2SO4,and a separating membrane made by coating a sheet of cellophane, assupplied by UCB film sector of Ghent, Belgium as 400 P Exp 389unplasticised film, with a solution obtained by mixing and dispersing 15parts by (dried) weight of hydroxyethyl cellulose obtained from UnionCarbide Corporation as "Cellosize: QP 100,000-H" in polyvinylidenechloride acrylate copolymer emulsion obtained from Unocal Chemicals as76 RES 917.

After charging the capacitor to a voltage of 2.7 Volts, with a constantcurrent of 19 mA, the pH of the anolyte was found to be about 1.7 whilethe catholyte was about 12. The charged electrochemical cell was thendischarged into a load resistor of 1000 Ohms yielding the expected RCexponential voltage decay as given in Table 7.

                  TABLE 7                                                         ______________________________________                                        Time                 Voltage                                                  ______________________________________                                        0.5 minutes          1.27 Volts                                               2                    1.10                                                     6                    0.66                                                     9                    0.54                                                     ______________________________________                                    

The magnitude of the total charge delivered into the load wasunexpected, however, being equivalent to the charge delivered by atheoretical capacitor with a capacity of about 0.5 Farad. This extremelyhigh capacitance with an area of only 4 cm2 would require an effectivedielectric constant of about 1,000,000,000,000.

EXAMPLE 42

The materials of this invention can furnish a surface with a reducedsliding coefficient of friction or increased lubricity when wetted orhydrolyzed.

It is well known that hydrogels become slippery when wet. For instancepoly(ethylene oxide) has been used to reduce the coefficient of frictionbetween flowing water and a fire hose to increased the rate of transferof water in fighting fires.

A friction reducing surface formed with a hydrogel is not, however,stable with time, i.e., the hydrogel will dissolve or leach out into thesurrounding media.

The materials for this invention can present a lubricious hydrogel richsurface which is stable in time due to the dispersion of the hydrogels,which minimizes the formation of soluble gels, and the bonding of thehydrogels to the inert supporting matrix. The materials can be applieddirectly to the surface by standard methods such as calendaring,coextrusion or solvent coatings and the like. The surface to be coatedcan be prepared or primed for the applied lubricious coating or coveringby first applying the matrix used in the final coating with reduced orno hydrogel content.

Such coatings should find application in liquid/solid interfaces wherereduced friction is desired such as on hulls of boats, fire or waterhose linings, pipe linings, liquid pumps and the like.

For example "guide wires" are used in medicine to guide cathetersthrough the veins and arteries. Such wires have an inherently highcoefficient of resistance which limits the depth and ease ofpenetration. It has been discovered that the lubricity can beconsiderably increased by coating the wire with 1) a prime coat ofpolyurethane resin supplied as HD-4610 supplied by C. L. Hauthaway &Sons Corporation and, after the prime coat has dried and cured, applying2) a second coating of a solution obtained by mixing and dispersing 15to 20 parts by (dried) weight of hydroxuethyl cellulose hydrogelobtained from Union Carbide Corporation as "Cellosize: QP 100,000-H"into an emulsion of an abrasion resistant matrix such as a polyurethaneresin supplied as HD-4610 supplied by C. L. Hauthaway & SonsCorporation.

While preferred embodiments of the present invention have been set forthfor purposes of illustration, the foregoing description should not bedeemed a limitation of the invention herein. Accordingly, variousmodifications, adaptations and alternatives may occur to one skilled inthe art without departing from the spirit and scope of the presentinvention.

What is claimed is:
 1. An electrode comprising:metallic electrodematerial; and a nonporous solid composite material encapsulating saidelectrode material, said composite material comprising an inert matrixmaterial having hydrogel substantially uniformly dispersed therein, thehydrogel comprising 10% to approximately 50% by weight of the drycomposite material, there being sufficient bonding between molecules ofthe hydrogel and the matrix material to prevent substantial leach-out ofhydrogel molecules from the composite.
 2. The electrode of claim 1wherein the electrode material comprises material selected from thegroup consisting of zinc, silver, lead, lead oxide, lead sulfate, zincoxide, copper, copper oxide, silver oxide, platinum, carbon andstainless steel.
 3. The electrode of claim 1 wherein the electrodematerial is dispersed within said composite material.
 4. The electrodeof claim 3 wherein the ratio of the weight of the composite material tothe electrode material is in the range of approximately 1.0 to 1.5. 5.The electrode of claim 1 further comprising a conductive materialdispersed within the composite material.
 6. The electrode of claim 1wherein the matrix material is selected from the group consisting ofpolyvinylidene chloride, polyvinyl chloride, polyvinylidene fluoride,polyethylene, polypropylene, polyurethane, vinyl acetate/ethylene, andphenol formaldehyde.
 7. The electrode of claim 6 wherein the hydrogel isa synthetic material selected from the group consisting of polyethyleneoxide, polyacrylic acid and polyacrylamide.
 8. The electrode of claim 6wherein the hydrogel is devised from natural materials selected from thegroup consisting of hydroxyethyl cellulose, gelatin, pectin, celluloseand starch.
 9. The electrode of claim 8 further comprising a couplingagent to facilitate the bonding between the hydrogel and the matrixmaterial.
 10. The electrode of claim 6 further comprising a couplingagent to facilitate the bonding between the hydrogel and the matrixmaterial.